Grassland management practices in Chinese steppes impact productivity, diversity and the relationship

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.

Contrasting effects of N fertilization and mowing on ecosystem multifunctionality in a meadow steppe

There is little experimental field evidence on how multiple essential land use intensification drivers(LUIDs),such as nitrogen(N)fertilization and mowing,interact to control ecosystem multifunctionality.Here,we conducted a 4-year field experiment in a meadow steppe in northeast China and evaluated the direct and indirect effects of mowing and N fertilization on a range of ecosystemfunctions associated with nutrient cycle,carbon stocks,and organic matter decomposition during the past 2 years of the experiment(2017 and 2018).Mowing had negative effects on the ecosystem multifunctionality index(EMF),carbon(C)cycle multifunctionality index(CCMF),and N cycle multifunctionality index(NCMF)in 2 years of sampling.However,in general,the responses of multifunctionality to N fertilization were ratespecific and year-dependent.N fertilization had positive effects on EMF,CCMF,NCMF,and phosphorus(P)cycle multifunctionality index(PCMF)in 2017,with the higher precipitation rate during the growing season,which was likely associated with the strong monsoon season.However,in 2018,EMF,CCMF,and NCMF increased at the lower N fertilization levels(£10 g N m^(-2) yr^(-1)),but decreased at higher N rates.N fertilization had consistent positive effects on PCMF in the 2 years of sampling.The effects of land use drivers on multifunctionality were indirectly influenced by bacterial biomass,plant richness,and soil moisture changes.Our results also indicated that the impacts of land use drivers on multifunctionality played an important role in maintaining a range of functions at low levels of functioning(<50% functional threshold).Low N fertilization levels(£10 g N m^(-2) yr^(-1))were able to reduce the negative effects of mowing on ecosystem multifunctionality while promoting plant biomass(food for livestock)and C storage.These findings are useful for designing practical strategies toward promoting multifunctionality by managing multiple LUIDs in a meadow steppe.

施肥草地刈割和放牧利用的研究

对黄土丘陵区的退化天然草地进行施肥处理，研究施肥草地在刈割、放牧利用下以种群生物量的季节动态和年动态的变化规律。为选择该地区最适宜的刈割期、刈割次数和放牧强度以及放牧次数对群落结构的影响提供理论依据。结果表明，在黄土丘陵干草原类型区，长芒草、百里香群落每年刈割两次（６月１５日、８月１０日），留茬高度４ｃｍ有利于草地的繁殖更新及个体形成。每年放牧两次（６月１０日、８月１０日），放牧强度每公顷１５只羊。