Abstract:

A field experiment of Medicago satial L. ‘Gannong No.3’ was arranged with four P addition of 0,80,120,160 Kg·hm^-2. Alfalfa was cut to 5 cm stubble height at the initial flowering stage of the second year, and cutting parts devided into three layers:from bottom to the third node as lower layer, from 4^th to 6^th node as middle layer, The seventh node and above as upper layer. Biomass of different layers and carbon(C),nitrogen(N) and phosphorous(P)of alfalfa leaf were tested to study the response to P addition. The results showed that the fresh weight of alfalfa at upper, middle and lower layer significantly increased with the increase of the amount of P,and the increase of lower layer was the largest, especially in the P addition of 120 Kg·hm^-2; C and P concentration of three layer leaves showed a positive correlation with the amount of P addition. The sensitivity of concentration of C, N and P of three layer leaves reduced from the upper to the lower. C:N, C:P and N:P in different layers showed a decreasing trend with the increase of the amount of P fertilizer. Compared with the control treatment, the maximum reduction of C:N was 120 Kg·hm^-2 P addition and the maximum reduction of C:P and N:P was 160 Kg·hm^-2 P addition; The increase of P fertilizer not only significantly increased the P absorption of alfalfa, but also promoted the absorption of alfalfa to C and N in different degrees; under 120 Kg·hm^-2 P treatment, the biomass of alfalfa N concentration of leaf reached the maximum, and the C and P concentration in three layer leaves reached a high level; according to N,P concentration and the stoichiometric ratios of N, P, alfalfa growth was limited by N and P initially, but it was gradually limited by N with the increase of the amount of P.

Key words: Alfalfa, Leaf, Layered, Biomass, Ecological stoichiometry, P addition

摘要：

以‘甘农3号’紫花苜蓿（Medicago satial L.‘Gannong No.3’）为材料，设计4个水平（0，80，120，160 Kg·hm^-2）的P添加田间试验，在种植第二年第一茬初花期留茬5 cm刈割，刈割部分从下到上以植株枝条第3茎节及以下作为下层，第4茎节至第6茎节作为中层，以第7茎节及以上作为上层，研究不同空间草层苜蓿生物量分布与叶片C，N，P化学计量特征对P添加的响应。结果表明：随着施P量的增加，苜蓿上、中、下3层生物量显著增加，且以下层的增幅最大，尤以120 kg·hm^-2的P添加量最为明显；上、中、下3层叶片C、P 含量与P添加量呈现正相关，施P增加了各层叶片C，N，P含量，且上、中、下3层叶片的C，N，P含量对P添加的敏感性由上到下依次递减；上、中、下3层叶片C：N，C：P和N：P均随着P添加量的增加呈现降低的趋势。与对照相比，各层叶片C：N在P添加120 Kg·hm^-2降幅最大，C：P和N：P 在P添加160 Kg·hm^-2降幅最大；P添加不仅显著增加苜蓿叶片对P的吸收，而且能不同程度地促进苜蓿叶片对C和N的吸收；在120 kg·hm^-2的P处理下，苜蓿生物量和叶片N含量达到最大，叶片C，P含量也达到较高水平；根据N，P含量与化学计量比来判断，研究区苜蓿生长受N和P共同限制，但随着P添加量的增加，苜蓿逐渐受到N限制。

关键词: 紫花苜蓿, 叶片, 分层, 生物量, 生态化学计量学, P添加