There is increasing interest in the potential of trees to sequester carbon (C) in above- and below-ground stocks to mitigate against increasing concentrations of greenhouse gases (GHG). This study determined whether pasture-tree (PT) systems influence soil C stocks compared with open pasture (OP) by sampling four sites with trees aged 14 to16 years. Poplars (Populus spp.) at Tikokino and Woodville and alders (Alnus spp.) at Poukawa and Ruakura were planted on contrasting soils (Haplustands, Endoaquepts, Durustalfs and Humaquepts, respectively). Trees at all four sites were arranged in partial-Nelder radial planting designs, with five stem densities ranging from 67 to 1276 stems ha-1. Soils were sampled at five stem density classes, along with adjacent OP areas in the same paddock, to a depth of 1 m (0-75, 75-150, 150-300, 300-600, 600-1000 mm). At three of the four sites, root mass density was greater (P < 0.05) in PT than in OP systems. At Woodville, estimates of total soil C mass to 1 m tended to be greater (P = 0.08) in the OP than in the PT system (200 vs. 163 Mg C ha-1, respectively), whereas no significant differences in total soil C masses between OP and PT were shown at the remaining sites (P > 0.10). Despite the limited statistical significance, estimates of total soil C mass at Tikokino and Woodville (sites with poplars) were 11 and 18% greater in OP than in PT systems, whereas estimates at Poukawa and Ruakura (sites with alders) were 2 and 6% greater in PT than in OP systems. Under the current conditions, our study suggests that tree species may be an additional factor influencing the C cycle and C accumulation in soils and need to be considered in the building of our soil C inventories.

中文翻译：

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放牧草地和牧场－树木系统下的土壤碳储量。

人们越来越关注树木在地下和地下储量中封存碳（C）以缓解温室气体（GHG）浓度增加的潜力。这项研究通过对年龄在14至16岁的树木进行采样，确定了与开放式牧场（OP）相比，牧场-树木（PT）系统是否影响土壤碳库。Tikokino和Woodville的杨树（Populus spp。）以及Poukawa和Ruakura的ders木（Alnus spp。）种植在对比土壤（分别为Haplustands，Endoaquepts，Durustalfs和Humaquepts）上。在所有四个地点的树木均按部分Nelder径向种植设计进行排列，五种茎密度介于67至1276个茎ha-1之间。在五个围栏密度级别以及同一围场中相邻的OP区域对土壤进行了采样，采样深度为1 m（0-75、75-150、150-300、300-600、600-1000 mm）。在四个部位中的三个部位，PT中的根质量密度大于OP系统中的根质量密度（P <0.05）。在伍德维尔，OP中的土壤总碳质量估计为1 m倾向于更大（P = 0.08）（分别为PT系统（200 vs. 163 Mg C ha-1）），而总土壤中无显着差异其余部位显示出OP和PT之间的C肿块（P> 0.10）。尽管统计意义有限，但OP中的Tikokino和Woodville（具有杨树的站点）的总土壤碳质量估计比PT系统高11和18％，而Poukawa和Ruakura（具有al木的站点）的估计总土壤C质量分别为2和6％在PT中比在OP系统中更大。在当前条件下，