黄土丘陵区氮磷添加对草地群落优势种养分利用特征的影响

为阐明黄土丘陵区氮磷添加对草地群落优势种养分利用特征的影响,探究群落结构和物种多样性的变化机制,选取5个典型优势种,即白羊草(Bothriochloa ischaemum)、长芒草(Stipa bungeana)、达乌里胡枝子(Lespedeza davurica)、铁杆蒿(Artemisia sacrorum)和猪毛蒿(Artemisia scoparia)为研究对象,采用裂区试验设计,以氮添加为主区处理, 包括:0(N0)、25(N25)、50(N50) 和100(N100) kg N hm^-2 a^-1;以磷添加为副区处理,包括:0(P0),20(P20),40(P40) 和80(P80) kg P₂O₅ hm^-2 a^-1,测定了各物种叶片氮磷比、氮磷重吸收效率、氮磷利用效率和相对生物量等参数。5种植物的氮和磷重吸收效率正相关,对氮磷添加量的响应具有耦合性。不同氮磷添加处理下,达乌里胡枝子叶片氮磷比最高,而氮磷重吸收效率最低;白羊草和长芒草的氮磷利用效率和重吸收效率高于其他物种。单施磷或N25与磷配施下,各物种相对生物量与氮磷比和磷利用效率呈正相关关系,与氮利用效率和氮磷重吸收效率呈负相关关系。单施氮、N50和N100与磷配施下,各物种相对生物量与氮磷利用效率和重吸收效率呈正相关,与氮磷比呈负相关。不施肥处理下,白羊草和长芒草相对生物量最高,低氮高磷下达乌里胡枝子相对生物量最高,高氮高磷下铁杆蒿和猪毛蒿相对生物量最高。不同优势种对氮磷添加的响应不同,生理生态过程各异,决定了其在群落中的优势度,这是氮磷添加后草地群落结构和物种多样性发生变化的关键机制。

Effects of nitrogen and phosphorus addition on nutrient use characteristics of grassland community dominant species in loess hilly-gully region

In order to elucidate the effects of nitrogen (N) and phosphorus (P) addition on nutrient utilization characteristics of grassland dominant species and explore the changes mechanism of grassland community structure and species diversity in loess hilly-gully region, five typical dominant species of common grassland communities including Bothriochloa ischaemum, Stipa bungeana, Lespedeza davurica, Artemisia sacrorum, and Artemisia scoparia, were selected as research objects. A split-plot N and P addition experiment was conducted, with N addition as the main-plot and P addition as the subplot [main-plot: 0 (N0), 25 (N25), 50 (N50), and 100 (N100) kg N hm^-2 a^-1; subplot: 0 (P0), 20(P20), 40 (P40), and 80 (P80) kg P₂O₅ hm^-2 a^-1]. The leaf N and P ratio, N use efficiency, P use efficiency, N reabsorption efficiency, P reabsorption efficiency, relative biomass and their relations of the five dominant species were investigated. Results showed that the reabsorption efficiency of N and P was positively correlated, and their response to N and P addition amount was coupled in each dominant species. Under different N and P additions, L. davurica had the highest leaf N and P ratio, but possessed the lowest N reabsorption efficiency and P reabsorption efficiency. Under different N and P additions, B. ischaemum and S. bungeana had higher N reabsorption efficiency, P reabsorption efficiency, N use efficiency and P use efficiency than other species. Under P addition alone and combined with N25, the relative biomass of each dominant species was positively correlated with leaf N and P ratio and P use efficiency, while negatively correlated with N use efficiency, N reabsorption efficiency and P reabsorption efficiency. The relative biomass of each dominant species showed positive relationships with N reabsorption efficiency, P reabsorption efficiency, N use efficiency and P use efficiency, while showed negative relationships with N and P ratio under N addition alone or N50 and N100 combined with P addition treatments. Under unfertilized condition, B. ischaemum and S. bungeana had the highest relative biomass. Under low N and high P conditions, L. davurica had the highest relative biomass, while A. sacrorum and A. scoparia had the highest relative biomass under high N and high P conditions. Different dominant species showed different physioecological processes in responses to N and/or P addition, which determined their dominance in the grassland community, and this is the key mechanism for the change of grassland community structure and species diversity after N and P addition.