放牧与围封对黄土高原典型草原植物生物量及其碳氮磷贮量的影响

 将黄土高原典型草原植物亚生态系分为地上活体、立枯物、凋落物和地下根系４个部分，进行放牧与围封草地植物生物量及其碳、氮、磷贮量的研究。结果表明，放牧与围封草地各组分碳、氮、磷贮量的季节动态模式与其对应生物量变化规律一致；碳、氮、磷贮量均与生物量呈极显著正相关（P＜０．０１），其相关系数分别为０．９９０，０．８９９和０．９３６（ＦＧ），０．９９０，０．８９１和０．９３６（ＧＧ）；封育和放牧草地植物间各部分碳、氮、磷贮量差异均由各自生物量差异引起。围封草地植物总生物量和地上、地下生物量、立枯物、凋落物的量，以及碳、氮、磷贮量一般高于放牧样地（P＜０．０５）。地上活体氮、磷贮量在其生物量最大时最高（７ 月），此时围封草地地上活体氮、磷贮量（１．２９１８，０．０８３７ｇ／ｍ^２）显著低于放牧草地（１．５２９７，０．１００２ｇ／ｍ^２）（P＜０．０５）。放牧草地主要通过地上幼嫩器官生物量和氮、磷含量的增加来获得较大氮磷贮量，并以此提高草地利用率。

Effects on plant biomass and CNP contents of plants in grazed and fenced steppe grasslands of the Loess Plateau

The plant subsystem in typical steppe grassland of the Loess Plateau was divided into four components: live shoots, standing dead matter, litter, and underground roots. The plant biomass of these four components and their C, N, and P contents were studied in grazed (GG) and fenced (FG) grasslands. The seasonal dynamics of each component biomass was correlated with their C, N and P contents both in grazed and fenced grasslands. There were significant positive correlations between plant biomass and C, N, and P contents, with correlation coefficients of 0.990, 0.899, 0.936 (FG) and 0.990, 0.891, 0.936 (GG), respectively. The differences in C, N, and P contents of each plant component were caused by the difference in plant biomass. The total biomass, aboveground and underground biomass, standing dead matter and litter, and their C, N, and P contents were significantly (P<0.05) higher in fenced grassland than those in grazed grassland. The N and P contents in live shoots were highest in July, and significantly (P<0.05) lower in fenced (1.291 8 and 0.083 7 g/m~2 for N and P respectively) than in grazed (1.529 7 and 0.100 2 g/m~2 for N and P respectively) grassland. The results indicate that the higher plant N, P storages in grazed grassland were mainly attributed to the increases of young organ biomass and their N, P contents, which further improve the utilization of grassland.