黄土丘陵区燕沟流域典型植物叶片C、N、P化学计量特征季节变化

以黄土丘陵区燕沟流域为例,分析了流域8种典型植物叶片C、N、P化学计量特征的季节变化。结果发现,8种植物叶片C含量分布范围在370.2-566.9 mg/g,N含量在9.2-39.0 mg/g,P含量在0.81-2.35 mg/g,C:N在10.5-52.9,C:P在186.8-667.5,N:P在5.7-23.0。叶片平均C、C:N和C:P在5月小于7月和9月(P<0.05),而在7月和9月差异不显著;N在5月大于7月和9月(P<0.05),7月和9月差异不显著;P在7月小于5月和9月(P<0.05),5月和9月差异不显著;N:P在9月明显小于5月和7月(P<0.05),5月和7月差异不显著。叶片C含量受季节因素影响显著,而在物种间差异不显著;叶片N、P、C:N、C:P、N:P受物种和季节因素影响均显著。因此,8种植物中沙棘、黄刺梅和虎榛子采用防御性的生活史策略;刺槐、柠条和狼牙刺采用竞争性生活史策略,铁杆蒿和茭蒿的生活史策略介于上述二者之间;尽管叶片N:P随生长季节发生明显变化,但研究区植物生长的限制性元素未随生长季节变化而改变。

Seasonal variations in leaf C, N, and P stoichiometry of typical plants in the Yangou watershed in the loess hilly gully region

Plants adjust their growth rate to adapt to environmental changes throughout their lives. The growth rate can be regulated by leaf carbon:nitrogen:phosphorus (C:N:P) ratios; therefore, these ratios reflect the adaptability of plants to the external environment. Seasonal variations in leaf C:N:P ratios reflect the seasonal variations of plant growth rate. Consequently, researches on the seasonal variations in leaf C:N:P ratios can increase our understanding of plant adaptation strategies. For studies on nutrient limitation within ecosystems, a rapid and accurate method to diagnose nutrient limitation is essential. The leaf N:P ratio at a particular plant growth stage is a convenient diagnostic method to determine which element is restricting plant growth. However, the leaf N and P contents and the N:P ratio change during the plant growing season, and this can complicate identification of the restricting element. Up until now, there has been little research on the change in limiting nutrients during the plant growing season. In this study, we monitored leaf C, N, and P stoichiometry of eight typical plant species in the Yangou watershed in the loess hilly gully region. The plant species were Quercus liaotungensis, Sophora davidii, Rosa xanthina, Ostryopsis davidiana, Artemisia sacrorum, Artemisia giraldii, Robinia pseudoacacia, Hippophae rhamnoides, and Caragana microphylla. We determined leaf C, N, and P stoichiometry at different growth stages from May to October 2007, and analyzed the effects of species and seasonal factors on leaf C:N:P stoichiometry. The leaf C, N and P contents of the eight plant species ranged from 370.2 to 566.9 mg/g, 9.2 to 39.0 mg/g, and 0.81 to 2.35 mg/g, respectively. The leaf C/N, C/P and N/P ratios ranged from 10.5 to 52.9, 186.8 to 667.5, and 5.7 to 23.0, respectively. The average leaf C contents and C:N and C:P ratios were markedly lower in May than in July and September, but not significantly different between July and September. The average leaf N contents were higher in May than in July and September, but not significantly different between July and September. The average leaf P contents were lower in July than in May and September, but not significantly different between May and September. The average leaf N:P ratio was lower in September than in May and July, but not significantly different between May and July. Species and seasonal factors showed significant effects on leaf N and P contents, and on C:N, C:P, and N:P ratios. In terms of leaf C contents, species had little effect but seasonal effects were significant. The results of this study indicate that (1) Hippophae rhamnoides, Rosa xanthina. and Ostryopsis davidiana adopted a defensive life history strategy; Robinia pseudoacacia, Caragana microphylla, and Sophora davidii adopted a competitive life history strategy; and Artemisia sacrorum and Artemisia giraldii adopted a life history strategy between the other two. (2) In the study area, the leaf N:P ratios clearly changed during the growth season, but the restrictive element in plant growth did not. Further research should be conducted to determine whether these trends occur over broader spatial scales and longer time scales.