塔克拉玛干沙漠南缘豆科与非豆科植物的氮分配

在豆科与非豆科植物光合特性的研究中发现,非豆科植物具有更高的光合速率,与其低的叶氮含量相矛盾。在沙漠中氮素是限制植物生长的关键因子之一,考虑到豆科植物的生物固氮作用和叶氮大部分分配于光合系统,我们假设:(1)非豆科植物具有更低的叶氮含量;(2)分配更少的叶氮于光合系统;(3)具有更高的最大净光合速率(Pmax)和光合氮素利用效率(PNUE)。为了验证这些假设,以塔克拉玛干沙漠南缘的豆科植物骆驼刺(Alhagi sparsifolia)和非豆科植物柽柳(Tamarix ramosissima)、花花柴(Karelinia caspica)为研究对象,比较了它们的叶氮含量、氮分配、Pmax和PNUE等。结果表明:(1)非豆科植物比豆科植物确实有更低的叶氮含量,且差异达到显著水平;(2)非豆科植物分配更少的叶氮于光合系统,但在光合系统内部具有更高效的氮分配机制;(3)非豆科植物具有更高的Pmax和PNUE。在光合系统内部,非豆科植物分配更多的叶氮于羧化系统,而豆科植物分配更多的叶氮于捕光系统。对于非豆科植物而言,其更高的Pmax、PNUE、水分利用效率和表观量子产量,取决于将更多的叶氮投入到羧化和电子传递系统中。这些生理优势决定了塔克拉玛干沙漠南缘非豆科植物高效的资源捕捉和利用能力。

Nitrogen allocation and partitioning within a leguminous and two non-leguminous plant species growing at the southern fringe of China's Taklamakan Desert

Aims We previously found that non-leguminous species had a higher photosynthetic rate despite lower leaf N content. Nitrogen is a critical factor limiting plant growth in the desert. Our objectives were to determine if, as hypothesized, non-leguminous species have lower leaf N content, allocate a lower fraction of leaf N to photosynthesis and have higher maximum net photosynthetic rate (P_max) and photosynthetic N-use efficiency (PNUE). Methods We compared the leguminous species Alhagi sparsifolia and non-leguminous species Karelinia caspica and Tamarix ramosissima in their typical habitat at the southern fringe of China’s Taklamakan Desert. Important findings As hypothesized, the non-leguminous species had significantly lower leaf N content and allocated a lower fraction of leaf N to photosynthesis. They also were more efficient in photosynthetic N partitioning. The non-leguminous species partitioned a higher fraction of the photosynthetic N to carboxylation and showed higher use efficiency of the photosynthetic N, while the leguminous species partitioned a higher fraction of the photosynthetic N to light-harvesting components. For the non-leguminous species, the higher fraction of leaf N allocated to carboxylation and bioenergetics led to higher P_max and therefore to higher PNUE, water-use efficiency and apparent quantum yield. These physiological advantages of the non-leguminous species and their higher leaf area ratio may contribute to their higher resource capture ability.