Cover illustration
A new integrated crop-livestock system approach of pastoral livestock production on the Qinghai–Tibetan Plateau (QTP) allows the livestock grazing on the natural grassland area during the short warm season and the mixed crop/pastoral area during the cold season. The approach demonstrates that the benefits brought by the combination of livestock, forage and agricultural byproducts from the three zones are beyond the sum of individual resources. This study shows that the new ap [Detail] ...
To mitigate the impacts of grassland degradation on the Qinghai–Tibetan Plateau (QTP), in recent decades China has been implementing large-scale conservation programs and has invested about 42 billion CNY (7 billion USD). However, these programs are faced with major challenges involving trade-offs between ecological function, livestock production and income of pastoralists. Scientific assessments, as well as technical and policy issues, have not fully captured the complex ecological, social and economic dynamics of the challenges facing grassland management on the QTP. Pastoral livestock production on the QTP is characterized by imbalance in both quality and quantity between livestock seasonal nutrient requirements and herbage production, which forces pastoralists to keep larger numbers of livestock for longer periods, leading to overgrazing. To solve these problems, an integrated crop-livestock system is promoted to improve the efficiency of livestock production and conserve natural grassland as well for a sustainable system for the QTP.
China has almost 400 Mhm2 of grasslands, 90% of which is considered degraded to varying degrees, on which 16 million herders depend for their livelihoods and many more indirectly, along the value-adding chain. Since 1950, average stocking rates across China have increased 4-fold. National policies have focused over recent decades on finding ways to rehabilitate the degraded grasslands, to sustain livestock production from them, and to improve the livelihoods of herder households, who are among the poorest people in China. A large collaborative program commenced in the early 2000s to help find solutions to the sustainable management of grasslands. This paper summarizes key findings of many research projects, identifies where knowledge is weak and argues that the successful rehabilitation of grasslands will also require policies that provide incentives and support for herders as they move from a focus on survival to a focus on production of higher quality products, for which consumers are increasingly willing to pay. A key focus is to emphasize the improvement of animal production per head. When this is done, it naturally leads to lower stocking rates, which in turn provides the opportunities for grasslands to recover. Across a range of experiments, farm demonstrations and analyses using models, in Inner Mongolia and Gansu, a consistent result has been that a 50% reduction in stocking rates, improves net household income and starts the process of grassland rehabilitation. Rather than focusing on stocking rates, better management of grasslands could be achieved by maintaining the grasslands above critical values for herbage mass, values that help optimize botanical composition, reduce soil erosion, optimize animal growth rates and aid ecosystem functions. Managing to critical values for herbage mass is likely to be more effective than efforts to calculate sustainable stocking rates. An early summer rest is valuable for aiding grassland rehabilitation and summer productivity, but a total grazing ban (typically for 5 years) may not achieve its aims as evidence shows it may take 10–15 years to achieve a better grassland state. Less-desirable plant species often increase in degraded grasslands that are rested and grazing can help manage those species. Surveys of herders indicate they have very mixed views on the benefits of total grazing bans that are unlikely to rehabilitate grasslands to an ideal botanical composition. The current objective is to work with grasslands that herders now have and optimize the existing composition. Grazing grasslands in winter results primarily in weight loss by animals and there is now evidence of how winter grazing reduces grassland growth in the next summer. It is better to keep animals in well-built sheds and feed them better, improved feeding through the cold months is required. In addition to the application of results from national programs designed to improve grasslands, it will be important to train herders as they move from survival to production, to foster the development of better markets for their livestock products, to devise better financial support for herder businesses and to revise land tenure arrangements so that herders can expand the area of land they graze on better terms than apply at present.
During the last few decades, there have been an increasing number of studies on grassland ecology in China, involving the classic ecology concepts or theories and the applicable ecological principles of grassland conservation or management. This paper reviews the main progress in the following aspects. (1) Research on grassland species adaptation and resistance, population dynamics and foraging behavior, and biodiversity and community stability. (2) Research on managed grassland ecosystems (grassland grazing ecology) including grazing effects on grassland ecosystem function and foraging behavior by large herbivores. (3) Global climate change and grassland processes and functioning. (4) Applied research on grassland restoration and ecosystem health assessments such as vegetation restoration, restoration of ecosystem functioning, and assessment methods. There have been significant advances in grassland ecology, including the functions of ecosystem biodiversity, the ecological stoichiometry mechanisms affecting grassland community stability, grazing regulation of plant diversity and nutrient cycling. Grassland ecologists have succeeded in making these advances through observational, experimental and theoretical studies. Nevertheless, there are still significant challenges for the grassland ecology research, including understanding of grassland spatial processes, grassland grazing and multi-functionality, integrated effects of global climate change across grassland areas, as well as the ecological methodology and experimental techniques in grassland ecology.
Grasslands are crucial parts of the terrestrial ecosystem, with an extremely high differentiation of productivity and diversity across spatial scales and land use patterns. The practices employed to manage grassland, such as grazing, haymaking, fertilization or reseeding, can improve the grassland condition. This study focuses on the changes in productivity and diversity and the relationship between them as affected by management practices. Productivity and diversity have unequivocally been altered in response to different management practices. When grazing intensity of a typical steppe increased from 1.5 to 9 sheep per hectare, both productivity and diversity declined. Higher grazing intensity (6 to 9 sheep per hectare) accelerated loss of diversity because of lower productivity. Productivity was significantly improved but diversity was lost by fertilizing. N fertilization also reduced the sensitivity of diversity to productivity. A similar response was found in mown grassland with increased productivity and diversity but their relationship was negatively affected. Mowing also slowed down the decline in diversity as productivity increased. Reseeding purple-flowered alfalfa led to an increased diversity, while yellow-flowered alfalfa increased productivity significantly. The negative productivity-diversity relationship was transformed to a positive one by reseeding alfalfa. These results enhance understanding of how productivity, diversity and their relationships change in response to altered grassland management practices, and support an integrated approach for improving both productivity and diversity.
Plant litter decomposition has been studied extensively in the context of both warming and increased atmospheric nitrogen deposition. However, the temporal patterns of mass loss and nutrient release in response to warming and nitrogen addition remain unclear. A 2-year decomposition experiment aimed to examine the effects of warming and nitrogen addition on decomposition rate, and nitrogen and phosphorus dynamics. The effects of warming and nitrogen addition on decomposition of litter of Stipa breviflora, a dominant species in a desert steppe of northern China, were studied. Warming and nitrogen addition significantly enhanced litter mass loss by 10% and 16%, respectively, and moreover promoted nitrogen and phosphorus release from the litter in the first year of decomposition, followed by an immobilization period. The interactive effects of warming and nitrogen addition on mass loss, nitrogen and phosphorus concentrations of litter were also found during the decomposition. This study indicates that warming and nitrogen addition increased litter mass loss through altering litter quality. These findings highlight that interactions between climate change and other global change factors could be highly important in driving decomposition responses.
Forage kochia (Bassia prostrata) is used for rangeland reclamation and livestock and wildlife forage, but limited research has been conducted on its seed production. Therefore, this research evaluated the effect of harvest date on seed weight, germination, and seed yield of forage kochia subspecies virescens and grisea. Seed was harvested from individual plants for 3 years during October, November, and December. October harvest had the lightest 100-seed weights, with the November harvest slightly heavier than December, for most accessions. Cultivar Snowstorm and breeding line Sahsel, both subsp. grisea, had the greatest 100-seed weights in November, 155 and 143 mg, respectively, whereas, cv. Immigrant (subsp. virescens), the standard for forage kochia, ranked among the least for 100-seed weight. For most accessions, germination was lowest from the October harvest (11%–43%), with greater germination with November and December harvested seeds (43%–64%). Viable seed yields were greatest in November with the exception of two accessions, which peaked in October, indicating earlier maturity. Results indicate that forage kochia usually reaches optimum seed maturity by early November, after plants are exposed to freezing temperatures; however, earlier maturing accessions exist in both subspecies virescens and grisea.
A pot experiment was conducted in a greenhouse with three alfalfa (Medicago sativa) cultivars, Aohan, Zhongmu No.1 and Sanditi, to examine the morphological and physiological responses of alfalfa to water stress. The response of alfalfa to water stress at different growth stages was generally similar, but varied among cultivars. At the branching, flowering and podding stages, the shoot biomasses of Aohan and Zhongmu No.1 were greatly affected by, and responded quickly to, water stress. The shoot biomass of Sanditi was not affected by mild water stress, but had a slight response to moderate and severe water stress. The root/shoot ratios in Aohan and Zhongmu No.1 were more sensitive to water stress than in Sanditi, with the root/shoot ratio in Aohan increasing most significantly. At flowering, the root/shoot ratio was the highest and the effect of water stress the greatest. The abscisic acid (ABA) concentration in the roots of Aohan and Zhongmu No.1 increased under water stress, while in Sanditi there was only a slight or delayed response of ABA concentration.
New Zealand is well known for export of meat and dairy products from low cost pastoral systems. These farm systems are continually evolving for increased efficiency, in part through the use of metabolic energy modeling tools by farmers and farm consultants to explore alternative farm system configurations and identify new efficiencies. One recent innovation is the introduction of a herb pasture area, such as plantain. We used metabolic energy modeling to quantify seasonal feed flows in two successive years in a New Zealand hill country farm system, and to analyze the impact of the introduction of an area of plantain. Models employed were a self-built Microsoft Excel spreadsheet and a commercial New Zealand farm systems modeling package, FARMAX. Herbage production, animal performance and financial results for a base farm scenario created from the average of survey data for hill farms in the southern North Island, and the same farm with 10% and 20% of the area in plantain for the years 2010–2011 and 2011–2012 were modeled. The self-built model performed similarly to the commercial model. The system configuration of the base farm stockpiles surplus autumn feed for release to animals in winter and also incorporates flexibility that confers resilience to interannual weather variation through varying dates animals are purchased or sold. The introduction of an area of plantain was predicted to increase herbage production, animal performance and financial returns. The predicted benefit was higher for the year 2010–2011 where a drought occurred in summer than for the following year with higher summer rainfall. This demonstrates the profitability of introducing a plantain area to New Zealand hill farm systems, and suggests plantain will assist to mitigate adverse effects of warmer and drier summer conditions associated with current climate change trends.
Caffeic acid O-methyltransferase (COMT) is a crucial enzyme that mainly methylates phenylpropanoid meta-hydroxyl of C5 in the biosynthesis of syringyl lignin in angiosperms. A putative COMT, named as PvCOMT1, was isolated from switchgrass (Panicum virgatum), a C4 warm-season dual-purpose forage and bioenergy crop. Our results showed that recombinant PvCOMT1 enzyme protein catalyzed the methylation of 5-OH coniferyl alcohol, 5-OH coniferaldehyde (CAld5H) and 5-OH ferulic acid. Further in vitro studies indicate that CAld5H can dominate COMT-mediated reactions by inhibiting the methylation of the other substrates. Transgenic switchgrass plants generated by an RNAi approach were further employed to study the function of COMT in internode lignification. A dramatic decrease in syringyl lignin units coupled with an obvious incorporation in 5-OH guaiacyl lignin units were observed in the COMT-RNAi transgenic plants. However, the constitutive suppression of COMT in switchgrass plants altered neither the pattern of lignin deposition along the stem nor the anatomical structure of internodes. Consistent with the biochemical characterization of PvCOMT1, a significant decrease in sinapaldehyde was found in the COMT-RNAi transgenic switchgrass plants, suggesting that CAld5H could be the optimal intermediate in the biosynthesis syringyl lignin.
Puccinellia tenuiflora is a typical salt-exclu-ding halophytic grass with strong salt-tolerance, which enhances tolerance by restricting Na+ influx as well as having a strong selectivity for K+ over Na+. The HAK5 K+ transporters generally modulate effective K+ acquisition in plants, especially under low K+ condition. In this study, PtHAK5 from P. tenuiflora was isolated by RT-PCR and characterized using yeast complementation. The results showed PtHAK5 consisted of 784 amino acids and shared over 80% homology with the identified high-affinity K+ transporter HAK5 from other higher plants. The expression of PtHAK5 rescued the K+-uptake-defective phenotype of yeast strain CY162. In conclusion, PtHAK5 is a candidate for mediating high-affinity K+ uptake under low K+ conditions.
Switchgrass (Panicum virgatum L.), as a model herbaceous crop species for bioenergy production, is targeted to improve biomass yield and feedstock quality. Plant height is a major component contributing to biomass yield. Accordingly, the objectives of this research were to analyze phenotypic variation for biomass and plant height and the association between them and to localize associated plant height QTLs. Two lowland switchgrass mapping populations, one selfed and another hybrid population established in the field at Perkins and Stillwater, Oklahoma, were deployed in the experiment for two years post establishment. Large genetic variation existed for plant biomass and height within the two populations. Plant height was positively correlated with biomass yield in the selfed population (r = 0.39, P<0.0001) and the hybrid population (r = 0.41, P<0.0001). In the selfed population, a joint analysis across all environments revealed 10 QTLs and separate analysis for each environment, collectively revealed 39 QTLs related to plant height. In the hybrid population, the joint analysis across overall environments revealed 35 QTLs and the separate analysis for each environment revealed 38 QTLs. The findings of this research contribute new information about the genetic control for plant height and will be useful for future plant breeding and genetic improvement programs in lowland switchgrass.
Physiological responses to low temperature were analyzed in a chilling-tolerant centipedegrass (Eremochloa ophiuroides) accession, Shao Guan (SG), in comparison to the commercial cultivar, Common. Lower levels of ion leakage and higher chlorophyll (Chl) concentration were observed in SG than in Common during chilling stress. The maximum photochemical efficiency, the actual photosystem II (PSII) efficiency, photochemical quenching efficiency, and net photosynthetic rate were decreased during chilling stress in both genotypes, with higher levels of these parameters shown by SG than Common. In addition, higher activities of superoxide dismutase (SOD), catalase (CAT), ascorbate-peroxidase (APX) and glutathione reductase (GR), and higher concentrations of ascorbic acid (AsA) and glutathione (GSH) were observed in SG than in Common. Moreover, higher concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm) were observed in SG than in Common. Correlation analysis indicated that SOD, CAT, APX and GR activities, and AsA and GSH concentrations showed high correlation to Put, while APX, GR, and AsA concentrations were correlated to Spd. Exogenous Put or Spd increased antioxidant enzyme activities and chilling tolerance. The results suggested that polyamine-regulated antioxidants are important for chilling tolerance in centipedegrass and protect plants against chilling induced oxidative damage.
We conducted 30- and 60-d greenhouse experiments to compare functional traits of Bromus tectorum (invasive annual grass) and four perennial bunchgrasses under well-watered or drought conditions. Even under drought, B. tectorum experienced significantly less stress (i.e., higher xylem pressure potential and greater shoot water content, water use per day and water-use efficiency) and biomass production than the perennial grasses after 30 d. However, after 60 d, its superiority was reduced under infrequent watering. Differences among perennial grasses were more pronounced for physiological traits under infrequent watering and for morphological traits under frequent watering. Elymus multisetus (fast-growing species) had a higher transpiration rate, lower leaf temperature, and lower water-use efficiency than the other grasses after 30 d. In contrast, Pseudoroegneria spicata (slow-growing) had lower xylem pressure potential and higher leaf temperature than all other grasses under infrequent watering. Under frequent watering, shoot dry mass and specific leaf area of B. tectorum was matched by Elymus wawawaiensis (moderate-growing species). Our results indicate that multiple-species plantings or seedings are necessary to foster greater weed resistance against B. tectorum. We also emphasize that when choosing plant material for restoration, performance during both pulse (resource-rich) and inter-pulse (resource-poor) periods should be considered.
Fungal endophytes of some cultivated grasses can increase plant performance and competitive abilities, especially under stress. Far less is known about the influence of Epichloë infections in wild populations of wild grasses. In this study, plants of three Elymus dahuricus ecotypes (WLS, QY and WTS) either infected with Epichloë endophyte (E+) or uninfected (E–) were grown in the field. The activities of the antioxidant enzymes ascorbate peroxidase, catalase, peroxidase and superoxide dismutase, and concentrations of H2O2 and malondialdehyde were examined in the leaves of E+ and E– plants. We also determined photosynthesis parameters, leaf blade and sheath carbohydrate concentration and plant growth parameters of both E+ and E– plants. E+ plants from the WLS and QY populations had significantly higher antioxidant enzyme activities and photosynthetic capability (P<0.05), superior growth characteristics including more abundant carbohydrate concentration than E– plants. In contrast, in plants from the WTS population, the endophyte had no significant effect on reactive oxygen species scavenging capability and growth performance (P>0.05), and even displayed some negative effects on plant photosynthetic capability. Thus, endophyte infection significantly affected E. dahuricus antioxidant enzyme activities (P<0.05), photosynthesis and growth capability, although, the effects varied with plant ecotypes.