Schutz Alexander Ernest Noel, Bond William J, Cramer Michael D
Botany Department, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.
Oecologia. 2009 May;160(2):235-46. doi: 10.1007/s00442-009-1293-1. Epub 2009 Feb 12.
In frequently burnt mesic savannas, trees can get trapped into a cycle of surviving fire-induced stem death (i.e. topkill) by resprouting, only to be topkilled again a year or two later. The ability of savanna saplings to resprout repeatedly after fire is a key component of recent models of tree-grass coexistence in savannas. This study investigated the carbon allocation and biomass partitioning patterns that enable a dominant savanna tree, Acacia karroo, to survive frequent and repeated topkill. Root starch depletion and replenishment, foliage recovery and photosynthesis of burnt and unburnt plants were compared over the first year after a burn. The concentration of starch in the roots of the burnt plants (0.08 +/- 0.01 g g(-1)) was half that of the unburnt plant (0.16 +/- 0.01 g g(-1)) at the end of the first growing season after topkill. However, root starch reserves of the burnt plants were replenished over the dry season and matched that of unburnt plants within 1 year after topkill. The leaf area of resprouting plants recovered to match that of unburnt plants within 4-5 months after topkill. Shoot growth of resprouting plants was restricted to the first few months of the wet season, whereas photosynthetic rates remained high into the dry season, allowing replenishment of root starch reserves. (14)C labeling showed that reserves were initially utilized for shoot growth after topkill. The rapid foliage recovery and the replenishment of reserves within a single year after topkill implies that A. karroo is well adapted to survive recurrent topkill and is poised to take advantage of unusually long fire-free intervals to grow into adults. This paper provides some of the first empirical evidence to explain how savanna trees in frequently burnt savannas are able to withstand frequent burning as juveniles and survive to become adults.
在频繁燃烧的湿润稀树草原中，树木可能会陷入一个循环：通过重新抽芽在火灾导致的茎干死亡（即地上部分死亡）中存活下来，但一两年后又会再次遭受地上部分死亡。稀树草原树苗在火灾后反复重新抽芽的能力是近期稀树草原树木与草本植物共存模型的关键组成部分。本研究调查了碳分配和生物量分配模式，这些模式使稀树草原的优势树种——卡鲁金合欢能够在频繁且反复的地上部分死亡中存活。在火灾后的第一年，比较了火烧和未火烧植物的根淀粉消耗与补充、叶片恢复和光合作用情况。在地上部分死亡后的第一个生长季节结束时，火烧植物根部的淀粉浓度（0.08±0.01克/克）仅为未火烧植物（0.16±0.01克/克）的一半。然而，火烧植物的根淀粉储备在旱季得到补充，在地上部分死亡后的1年内与未火烧植物的储备量相当。重新抽芽植物的叶面积在地上部分死亡后的4 - 5个月内恢复到与未火烧植物相当的水平。重新抽芽植物的地上部分生长仅限于雨季的前几个月，而光合速率在旱季仍保持较高水平，这使得根淀粉储备得以补充。¹⁴C标记显示，储备最初在地上部分死亡后用于地上部分生长。地上部分死亡后一年内叶片的快速恢复和储备的补充表明，卡鲁金合欢非常适应在反复的地上部分死亡中存活，并准备利用异常长的无火间隔期成长为成年树木。本文提供了一些首批实证证据，以解释频繁燃烧的稀树草原中的树木如何能够在幼年时经受频繁燃烧并存活至成年。
