Results of several long-term studies of non-woody litter decomposition in forests indicate that we need to rethink why and how we measure rates of litter decomposition. Effects on litter decomposition rates were postulated to explain some of the nutritional effects of factors such as tree species, forest harvesting and fertilization. However, the accumulated experimental evidence indicates that litter decomposition rates do not mediate these responses. Many studies have reported litter mass loss becoming extremely slow at values considerably below 100%, indicating that early decay rates may not accurately foreshadow the entire decay process. Exclusion of soil faunal activities from current measurements of decomposition rates seriously reduces the likelihood that we are properly modeling decomposition. Finally, the use of regression and correlation analyses to determine which climate or initial litter quality factors control decay rate has led to many unwarranted and potentially misleading conclusions. These concerns are illustrated with examples from a suite of litter decomposition studies in British Columbia, Canada. Insights into nutrient cycling and carbon storage in ecosystems are more likely to arise from measuring the mass and nutrient content of annual litter input and determining the maximum decomposition limit and nutrient content at that stage, than by measuring early rates of decay. Improved predictions of relative decay rates of plant litters are likely to arise from a holistic approach based on plant life attributes rather than correlations based on individual initial litter chemistry parameters. Finally, a better understanding of the fate of faecal material of soil fauna is necessary before we can accurately predict and model litter decomposition. 相似文献
The long-term nature of forest crop rotations makes it difficult to determine impacts of forestry on soil nutrients that might be depleted by forest growth. We used small scale, highly stocked plots to compress the length of the rotation and rapidly induce nutrient depletion. In the study, two species (Pinus radiata D. Don and Cupressus lusitanica Miller) are compared under two disturbance regimes (soil undisturbed and compacted), and two fertiliser treatments (nil and plus fertiliser), applied in factorial combination at 33 sites, covering the range of climatic and edaphic variation found in plantation forests across New Zealand. To assess our ability to rapidly highlight important soil properties, foliar nutrient concentrations were determined 20 months after planting. It was hypothesised that the densely planted plots, even at a young age, would create sufficient pressure on nutrient resources to allow development of relationships between properties used as indicies of soil nutrient availability and foliar nutrient concentrations. For both species significant relationships between foliar nutrients and 0–10 cm layer soil properties from unfertilised plots were evident for N (total and mineralisable N) and P (total, acid extractable, organic, Bray-2 and Olsen P). With the exception of Ca in C. lusitanica, foliar K, Ca and Mg were correlated with their respective soil exchangeable cation measures. The results thus confirm the utility of the experimental approach and the relevance of the measured soil properties for forest productivity.
In unfertilised plots foliar N and P concentrations in P. radiata exceeded those in C. lusitanica, the differences being eliminated by fertiliser application. Foliar N/P ratios in P. radiata also exceeded those in C. lusitanica. In contrast to N and P, foliar K, Ca and Mg concentrations were all higher in C. lusitanica, the difference being particularly marked for Ca and Mg. P. radiata contained substantially higher concentrations of the metals Zn, Mn and Al than C. lusitanica, whereas the latter contained higher B concentrations. Possible reasons for differences between species in foliar nutrient concentrations are discussed. 相似文献
Mineral fertilizers were applied to adjacent plantations of 2, 4-year old, hybrid poplars: clone 27 (Northwest, P. deltoides × P. balsamifera) and 794 (Brooks, P. deltoides × P. × petrowskyana), in north eastern Alberta. Fertilization was done in May 2003 to see whether growth rates could be increased and rotations
shortened. Three fertilizers (N, NP and NPKS + Cu + Zn) were applied at each of three rates (supplying N at 0, 100 and 200 kg ha−1) in a factorial randomized block design to the two separate plantations. Fertilization with 200 kg ha−1 N and 100 kg ha−1 P increased volume growth of clone 27 by 1 m3 ha−1 year−1 over 2 years. Clone 794 showed no volume response to fertilization, but produced 8.7 m3 ha−1 more than clone 27. Leaf area, dry mass and nutrient concentrations of both clones increased in the first year after fertilization,
showing that fertilizer uptake occurred. Decrease in leaf size between 2003 and 2004 was affected by fertilizer level in clone
794. There were differences between some nutrient concentrations in the soils occupied by the two clones, and clone 794 had
higher leaf concentrations of N, K, Ca, S, Mn, Zn, B and Mo than clone 27. Fertilization of 4-year old plantations of either
clone was unwarranted, and planting clone 794 would be likely to provide greater yield than planting and fertilizing clone
27. 相似文献