Root biomass, turnover and net primary productivity of a coffee agroforestry system in Costa Rica: effects of soil depth, shade trees, distance to row and coffee age
Root biomass, turnover and net primary productivity of a coffee agroforestry system in Costa Rica: effects of soil depth, shade trees, distance to row and coffee age
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DOI：
10.1093/aob/mcw153
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发表时间：
2016-10-01
期刊：
影响因子：
4.2
通讯作者：
Jourdan, Christophe
中科院分区：
文献类型：
--
作者：
Defrenet, Elsa;Roupsard, Olivier;Jourdan, Christophe
背景和目的在哥斯达黎加，咖啡(Coffea Arabica)植物通常生长在农林中。然而，目前尚不清楚遮荫诱导树是否通过根系竞争降低了咖啡树的生物量，从而改变了总体净第一性生产力(NPP)。我们在林分水平上估算了生物量和净初级生产力，考虑了深根和植物在树上的位置。方法测定了咖啡/乔木混交林的树干生长和根的生物量、周转和分解。在一定的植株大小范围内，估计了生长轮的宽度和茎基数以及茎的断面积。根生物量和细根密度是在4米深的沟中测量的。为了考虑到农林复合系统的地下异质性，在一年多的时间里，通过连续的土壤去芯(深度30厘米)，在不同的位置(充分阳光下或树下和行/行间)测量了细根周转。利用异速生长关系来计算多年生成分的净初级生产力，然后将其放大到林分水平。关键结果随着树龄的增加，茎基年轮宽度增加到2.5 mm yr(-1)。咖啡根生物量几乎全部(92%)位于地表1.5m处，1.5m至4m处仅占8%，多年生木本植物根生物量为16tha(-1)，多年生植物根NPP为1.3tha(-1)a-1。细根生物量(0~30 cm)行内比行间高2倍。细根生物量为2.29 t ha(-1)，占总根生物量的12%，年净初级生产力为2.96 t ha(-1)，占总根生物量的69%。细根周转率为1.3年(-1)，寿命为0.8a。结论咖啡根系占植物总生物量的49%，这可能是修剪枝条的结果。不同树种对咖啡细根生物量的影响不显著，说明咖啡根系在表土中具有很强的竞争力。
Background and Aims In Costa Rica, coffee (Coffea arabica) plants are often grown in agroforests. However, it is not known if shade-inducing trees reduce coffee plant biomass through root competition, and hence alter overall net primary productivity (NPP). We estimated biomass and NPP at the stand level, taking into account deep roots and the position of plants with regard to trees.Methods Stem growth and root biomass, turnover and decomposition were measured in mixed coffee/tree (Erythrina poeppigiana) plantations. Growth ring width and number at the stem base were estimated along with stem basal area on a range of plant sizes. Root biomass and fine root density were measured in trenches to a depth of 4 m. To take into account the below-ground heterogeneity of the agroforestry system, fine root turnover was measured by sequential soil coring (to a depth of 30 cm) over 1 year and at different locations (in full sun or under trees and in rows/inter-rows). Allometric relationships were used to calculate NPP of perennial components, which was then scaled up to the stand level.Key Results Annual ring width at the stem base increased up to 2.5 mm yr(-1) with plant age (over a 44-year period). Nearly all (92 %) coffee root biomass was located in the top 1.5 m, and only 8 % from 1.5 m to a depth of 4 m. Perennial woody root biomass was 16 t ha(-1) and NPP of perennial roots was 1.3 t ha(-1) yr(-1). Fine root biomass (0-30 cm) was two-fold higher in the row compared with between rows. Fine root biomass was 2.29 t ha(-1) (12 % of total root biomass) and NPP of fine roots was 2.96 t ha(-1) yr(-1) (69 % of total root NPP). Fine root turnover was 1.3 yr(-1) and lifespan was 0.8 years.Conclusions Coffee root systems comprised 49 % of the total plant biomass; such a high ratio is possibly a consequence of shoot pruning. There was no significant effect of trees on coffee fine root biomass, suggesting that coffee root systems are very competitive in the topsoil.