Frank Yonghong Li

Modelling the seasonal and geographical pattern of pasture production in New Zealand

The pasture growth module AgPasture was integrated into the APSIM (Agricultural Production System Simulator) simulation model, allowing pasture-based systems to be modelled in combination with other land uses at farm scale or within land use change studies. The models predictions of pasture growth were evaluated against 32 pasture growth datasets from a diverse range of soil types and climatic zones across New Zealand. The pasture herbage accumulation simulated by the model closely matched actual measurements over varying intervals. Both predicted and measured pasture growth rate demonstrated the same seasonal pattern, including mean growth rate and inter-annual variation across measurement years. Predicted and measured annual average net herbage accumulation (NHA) on a dryland pasture was similar over 37 observation years (mean, 6.83 and 7.27 t DM/ha respectively; coefficient of variation, 29% and 27% respectively) and highly correlated (R 2 = 0.838, P < 0.0001; relative root mean squared deviation (RMSD) = 16%). The models prediction of annual average NHA of all simulated pastures, spanning a wide range of pasture environments, also matched the measurement data well (R 2 = 0.777, P < 0.0001; relative RMSD = 21%). However, discrepancies between simulated and observed values occurred in some seasons and at some sites. Analysis of these discrepancies identified areas where the model could be improved by incorporating more accurate descriptions of the effects of plant development and grazing, soil temperature and the interactive effects of high temperature and soil moisture dynamics.

The perception and adaptation of herdsmen to climate change and climate variability in the desert steppe region of northern China

The herdsmen in the desert steppe region in Northern China live primarily on the native rangelands. The semiarid climate has a profound impact on the economy and the livelihood of rural communities. Adaptation to the highly variable climate is the norm in pastoral management in the region but the increasing aridity and variability projected by climate change models provides new challenges for sustainable living in the harsh environment. The study surveyed the herdsmen’s perception of climate change and variability in the desert steppe region of Inner Mongolia, and compared it with the observed climatic patterns and the recorded disastrous climatic events. The existing rangeland and livestock management strategies used by local herdsmen to cope with variable climate were also investigated in order to assist in the development of better management adaptation strategies. The herdsman perceived temperature changes over the past 30 years, which matched well with the meteorological observations, while their perceived change in precipitation (decrease) did not agree with the meteorological records (no change). The discrepancy between the observed and perceived precipitation changes may have arisen from the combination of large seasonal and inter-annual fluctuation of precipitation, more recent drought years and a herdsmen’s desire to have a ‘wet year’, and more forage demand from increased livestock numbers. Herdsmen also had a reasonably good perception of strong wind/dust storms and snow storms, and their sensitivity to these extreme disastrous climatic events appeared to be related to the perception of drought. The herdsmen had better perceptions of recent short-term climate change and possibly to use it to assess the long-term changes. The major adaptive management strategies to cope with disastrous climatic events included selling livestock, buying feed, seeking other grazing resources, housing livestock and looking for other alternative jobs to compensate for the economic loss. Grazing other resources, either the reserved winter rangelands in the growing season in current household farm systems or the common winter rangelands in a traditional nomadic system, played a vital role in buffering the effects of extreme climatic events. Setting appropriate stocking rates and growing forage crops in suitable land areas may contribute to increasing the resilience of rangeland systems. Raising the herdsmen’s awareness of long-term climate change and its effects on rangelands is needed to improve their preparedness to adapt to the future climate.

Effects of mowing regimes and climate variability on hay production of Leymus chinensis (Trin.) Tzvelev grassland in northern China

Leymus chinensis (Trin.) Tzvelev grassland is the most widely distributed native steppe vegetation type suitable for haymaking in the semiarid pastoral regions of north-east Asia. The long-term effects of four mowing regimes (mowing once a year, twice a year, once every 2 years and twice every 3 years), and climatic variability on the hay production from L. chinensis grassland were investigated using permanent plots over 27 years. The results showed that (i) the overall cumulative annual herbage production over the 27 years was the highest under ‘mowing once a year’, and ‘mowing twice a year’ did not produce any significant change in the amount of harvested herbage; (ii) mowing induced a reduction in herbage production mostly in the first couple of years, and the reduction was larger under frequent than less frequent mowing. The annual herbage production in harvest years was higher under less frequent mowing (once every 2 years, or twice every 3 years) than that under annual mowing, but the higher herbage production in harvest years under less frequent mowing could not compensate for the herbage not made into hay in the years without harvest; (iii) annual herbage production generally increased with annual precipitation, but the response of annual herbage production to precipitation was best described by quadratic (instead of linear or logarithmic) equations, which suggested a decline in annual herbage production under the highest annual precipitation in the region, and the relationships stood under different mowing regimes; and (iv) an analysis of hay yield and quality, and costs of the mowing operation, showed that the haymaking from L. chinensis grassland was financially viable as long as the herbage production was not extremely low under drought. It is concluded that the best practice for haymaking from L. chinensis grassland should be based on the rule of ‘mowing once a year’ in high-production years and grazing in low-production years; and a light grazing early in the season may increase hay quality mowed in the autumn if the grassland grows well early in the season in high-production years.

Alpha, Beta and Gamma Diversity Differ in Response to Precipitation in the Inner Mongolia Grassland

Understanding the distribution pattern and maintenance mechanism of species diversity along environmental gradients is essential for developing biodiversity conservation strategies under environmental change. We have surveyed the species diversity at 192 vegetation sites across different steppe zones in Inner Mongolia, China. We analysed the total species diversity (γ diversity) and its composition (α diversity and β diversity) of different steppe types, and their changes along a precipitation gradient. Our results showed that (i) β diversity contributed more than α diversity to the total (γ) diversity in the Inner Mongolia grassland; the contribution of β diversity increased with precipitation, thus the species-rich (meadow steppe) grassland had greater contribution of β diversity than species-poor (desert steppe) grassland. (ii) All α, β and γ species diversity increased significantly (P<0.05) with precipitation, but their sensitivity to precipitation (diversity change per mm precipitation increase) was different between the steppe types. The sensitivity of α diversity of different steppe community types was negatively (P<0.05) correlated with mean annual precipitation, whereas the sensitivity of β and γ diversity showed no trend along the precipitation gradient (P>0.10). (iii) The α diversity increased logarithmically, while β diversity increased exponentially, with γ diversity. Our results suggest that for local species diversity patterns, the site species pool is more important in lower precipitation areas, while local ecological processes are more important in high precipitation areas. In addition, for β diversity maintenance niche processes and diffusion processes are more important in low and high precipitation areas, respectively. Our results imply that a policy of “multiple small reserves” is better than one of a “single large reserve” for conserving species diversity of a steppe ecosystem, and indicate an urgent need to develop management strategies for climate-sensitive desert steppe ecosystem.

Can Shallow Plowing and Harrowing Facilitate Restoration of Leymus chinensis Grassland? Results From a 24-Year Monitoring Program

Abstract Long-term effects of two mechanical interventions, shallow plowing and harrowing, on degraded Leymus chinensis (Trin.) Tzvel. grassland were studied. Species composition and standing biomass of the grassland were monitored at peak biomass each year for 24 yr after application of these two measures, together with grassland in natural recovery and that under public grazing. Results showed a high resilience of degraded grassland, which recovered naturally after excluding grazing animals to a structure similar to the intact L. chinensis community. In comparison with natural recovery, harrowing facilitated restoration of L. chinensis population and community structure and improved grassland production. Shallow plowing accelerated recovery of L. chinensis population to a larger extent than harrowing and led to a flourish of annual species and improvement of herbage production in the years following its application. But the production improvement was unsustainable and was associated with a decrease in grassland species richness and community complexity. We conclude that the best measure for restoring degraded grassland depends on the restoration objectives and severity of grassland degradation. Harrowing is a feasible technique to assist restoration of the degraded grassland. In contrast, shallow plowing is not appropriate for ecological restoration, but may be applied for quick restoration of herbage production.

Functional dominance rather than taxonomic diversity and functional diversity mainly affects community aboveground biomass in the Inner Mongolia grassland

Abstract The relationship between biodiversity and productivity has been a hot topic in ecology. However, the relative importance of taxonomic diversity and functional characteristics (including functional dominance and functional diversity) in maintaining community productivity and the underlying mechanisms (including selection and complementarity effects) of the relationship between diversity and community productivity have been widely controversial. In this study, 194 sites were surveyed in five grassland types along a precipitation gradient in the Inner Mongolia grassland of China. The relationships between taxonomic diversity (species richness and the Shannon–Weaver index), functional dominance (the community‐weighted mean of four plant traits), functional diversity (Raos quadratic entropy), and community aboveground biomass were analyzed. The results showed that (1) taxonomic diversity, functional dominance, functional diversity, and community aboveground biomass all increased from low to high precipitation grassland types; (2) there were significant positive linear relationships between taxonomic diversity, functional dominance, functional diversity, and community aboveground biomass; (3) the effect of functional characteristics on community aboveground biomass is greater than that of taxonomic diversity; and (4) community aboveground biomass depends on the community‐weighted mean plant height, which explained 57.1% of the variation in the community aboveground biomass. Our results suggested that functional dominance rather than taxonomic diversity and functional diversity mainly determines community productivity and that the selection effect plays a dominant role in maintaining the relationship between biodiversity and community productivity in the Inner Mongolia grassland.

Functional Redundancy Instead of Species Redundancy Determines Community Stability in a Typical Steppe of Inner Mongolia.

Background The redundancy hypothesis predicts that the species redundancy in a plant community enhances community stability. However, numerous studies in recent years questioned the positive correlation between redundancy and stability. Methodology We explored the relationship between the species redundancy, functional redundancy and community stability in typical steppe grassland in Northern China by sampling grassland vegetation along a gradient of resource availability caused by micro-topography. We aimed to test whether community redundancy enhanced community stability, and to quantify the relative importance of species redundancy and functional redundancy in maintaining community stability. Results Our results showed that the spatial stability of plant community production increases with increased supply of soil resources, and the functional redundancy instead of species diversity or species redundancy is correlated with the community stability. Our results supported the redundancy hypothesis and have implications for sustainable grassland management.

Phytolith-occluded organic carbon as a mechanism for long-term carbon sequestration in a typical steppe: The predominant role of belowground productivity

Phytolith-occluded organic carbon (phytOC) has recently been demonstrated to be an important terrestrial carbon (C) fraction resistant to decomposition and thus has potential for long-term C sequestration. Existing studies show that plant leaves and sheath normally have high phytOC concentration, thus most of phytOC studies are limited to the aboveground plant parts. Grassland communities comprise herbaceous species, especially grasses and sedges which have relatively high concentrations of phytoliths, but the phytOC production from grassland, especially from its belowground part, is unknown. Here we determined the phytOC concentration in different parts of major plant species in a typical steppe grassland on the Mongolian Plateau, and estimated the phytolith C sequestration potential. We found that the phytOC concentration of major steppe species was significantly (p<0.05) higher in belowground (0.67gkg-1) than aboveground biomass (0.20gkg-1) and that the belowground net primary productivity (BNPP) was 8-15 times the aboveground net primary productivity (ANPP). Consequently, the phytOC stock in belowground biomass (12.50kgha-1) was about 40 times of that in aboveground biomass (0.31kgha-1), and phytOC production flux from BNPP (8.1-15.8kgha-1yr-1) was 25-51 times of that from ANPP. Our results indicate that BNPP plays a dominant role in the biogeochemical silica cycle and associated phytOC production in grassland ecosystems, and suggests that potential phytolith C sequestration of grasslands may be at least one order of magnitude greater than the previous estimation based on ANPP only. Our results emphasize the need for more research on phytolith and phytOC distribution and flux in both above and below ground plant parts for quantifying the phytolith C sequestration.

Recovery succession drives the convergence, and grazing versus fencing drives the divergence of plant and soil N/P stoichiometry in a semiarid steppe of Inner Mongolia

Background and aimsUnderstanding the plant and soil elemental stoichiometry during grassland dynamics is important for developing measures to enhance the restoration of degraded grassland. A number of restoration practices have been applied in the degraded typical steppe grassland in Inner Mongolia, either for research purpose or as actual restoration projects. However, the effects of different restoration measures on soil and plant N/P stoichiometry remain unclear.MethodsHere we explored the effects of three restoration measures (i.e., natural recovery, NR; shallow ploughing, SP; and harrowing HA) on the N, P stoichiometry of plant and soil in a typical steppe of Inner Mongolia, by comparing plant and soil N, P content and N/P ratio among the grasslands restored through NA, SP and HA, and that under sustained animal grazing (GR).ResultsLong-term restoration increased aboveground plant biomass, litter accumulation and changed soil and plant N/P ratio. Soil N and P contents in restored grassland (NR, SP or HA) were higher than those under grazing (GR); the restored grasslands shared a common slope of N-P linear regression, which was significantly greater than that of grazing grassland. Plant N content and N/P ratio decreased firstly and then increased during the restoration of degraded grassland.ConclusionSoil N limitation is greater than soil P limitation in typical steppe of Inner Mongolia. Soil N limitation is smaller in naturally recovered grassland and grazing grassland than in the restored grassland following shallow ploughing and harrowing. The restoration succession over 26-years after the exclusion of animal grazing have changed the N-P coupling relation in grassland soil, with a common N-P relation converged under grassland that are treated with different restoration measures.

Mowing and topography effects on microorganisms and nitrogen transformation processes responsible for nitrous oxide emissions in semi-arid grassland of Inner Mongolia

PurposeFew studies have been done to investigate the impact of mowing on N2O emissions and the abundance of functional microbial genes, especially in sloping landscapes. This study aims to explore the impact of mowing on key N2O-producing processes under different topographical conditions in a semi-arid grassland.Materials and methodsSoil samples were collected from a semiarid grassland ecosystem in Xilingol region, Inner Mongolia, where long-term management practices including non-mowing and mowing in flat and sloping blocks were conducted. We then determined (1) soil moisture, total carbon (TC) and nitrogen (TN), and mineral N (NH4+-N and NO3−-N) content; (2) the potential N2O emission from nitrification (NN2O) and from denitrification (DN2O) and potential N2 emission (DN2); and (3) the gene abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), the narG (nitrate reductase) gene, and nosZ (nitrous oxide reductase) gene.Results and discussionSoil moisture and potential N2O emission from nitrification and denitrification were significantly lower in sloping than in flat conditions, whereas the TC, TN, NH4+-N, NO3−-N content, gene abundance of AOA, AOB, narG, and nosZ showed no difference between flat and sloping conditions. Mowing significantly decreased the gene abundance of AOA, AOB, narG in both flat and sloping areas, and significantly decreased potential N2O emissions, especially in sloping areas.ConclusionsThe potential N2O emission was significantly lower on sloping than flat grassland. Mowing significantly decreased the potential N2O emissions, especially on sloping grassland. Our results suggest that topographical conditions should be incorporated into methods for estimating N2O emission and land management practices in semiarid grassland.