Liu Zhiying, Baoyin Taogetao, Duan Junjie, Yang Guofeng, Sun Juan, Li Xiliang
Key Laboratory of Grassland Ecology, School of Ecology and Environment, Inner Mongolia University, Hohhot, China.
National Forage Improvement Center, Institute of Grassland Research, Chinese Academy of Agricultural Sciences, Hohhot, China.
Front Plant Sci. 2018 Mar 12;9:295. doi: 10.3389/fpls.2018.00295. eCollection 2018.
Identifying the linkages between nutrient properties and plant size is important for reducing uncertainty in understanding the mechanisms of plant phenotypic plasticity. Although the positive effects of grazing exclusion on plant morphological plasticity has been well documented, surprisingly little is known about the relationship of nutrient strategies with plant shoot size after long-term grazing exclusion. We experimentally investigated the impacts of grazing exclusion over time (0, 9, 15, and 35 years) on the relationships of nutrient traits (nutrient concentration, allocation, and stoichiometry) of with morphological plasticity in , which is a dominant species in grasslands of Inner Mongolia, China. Our results showed that there was a significantly negative correlation between the degrees of plasticity and stability of various morphological traits. Increases in plant size by 126.41, 164.17, and 247.47% were observed with the increase of grazing exclusion time of 9, 15, and 35 years, respectively. Plant size was negatively correlated with nitrogen (N) and phosphorus (P) concentrations, but was positively correlated with carbon (C) concentration. Biomass partitioning and leaf to stem ratios of nutrient concentrations contributed more than 95% of the changes in N, P, and C allocation in leaves and stems induced by grazing exclusions. Nine years' grazing exclusion rapidly changed the nutrient concentrations (averaged by -34.84%), leaf to stem nutrient allocations (averaged by -86.75%), and ecological stoichiometry (averaged by +46.54%) compared to free-grazing, whereas there was no significant trend of these nutrient traits across the 9, 15, and 35 years' grazing exclusion in individuals. Our findings suggest that with the increase of the duration of the grazing exclusion, time effects on plant performances gradually weakened both in plant morphological plasticity and nutrient properties. There is a significant negative effect between plant sizes and nutrient traits under long-term grazing exclusion.
确定养分特性与植物大小之间的联系对于减少理解植物表型可塑性机制的不确定性很重要。尽管放牧排除对植物形态可塑性的积极影响已有充分记录，但令人惊讶的是，对于长期放牧排除后养分策略与植物地上部分大小的关系却知之甚少。我们通过实验研究了不同时间（0、9、15和35年）的放牧排除对中国内蒙古草原优势物种羊草养分特性（养分浓度、分配和化学计量）与形态可塑性之间关系的影响。我们的结果表明，各种形态性状的可塑性程度与稳定性之间存在显著负相关。随着放牧排除时间分别增加9年、15年和35年，观察到植物大小分别增加了126.41%、164.17%和247.47%。植物大小与氮（N）和磷（P）浓度呈负相关，但与碳（C）浓度呈正相关。放牧排除引起的羊草叶片和茎中氮、磷和碳分配变化的95%以上是由养分浓度的生物量分配和叶茎比造成的。与自由放牧相比，9年的放牧排除迅速改变了养分浓度（平均降低34.84%）、叶茎养分分配（平均降低86.75%）和生态化学计量（平均增加46.54%），而在9年、15年和35年放牧排除的羊草个体中，这些养分特性没有显著变化趋势。我们的研究结果表明，随着放牧排除持续时间的增加，时间对植物性能在形态可塑性和养分特性方面的影响逐渐减弱。在长期放牧排除下，植物大小与养分特性之间存在显著负效应。
