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
Landscape Ecology - Maintaining biodiversity in multifunction landscapes is a significant challenge. Planning for the impacts of change requires knowledge of how species respond to landscape... 相似文献
Wild bee populations are currently under threat, which has led to recent efforts to increase pollinator habitat in North America. Simultaneously, U.S. federal energy policies are beginning to encourage perennial bioenergy cropping (PBC) systems, which have the potential to support native bees.
Objectives
Our objective was to explore the potentially interactive effects of crop composition, total PBC area, and PBC patches in different landscape configurations.
Methods
Using a spatially-explicit modeling approach, the Lonsdorf model, we simulated the impacts of three perennial bioenergy crops (PBC: willow, switchgrass, and prairie), three scenarios with different total PBC area (11.7, 23.5 and 28.8% of agricultural land converted to PBC) and two types of landscape configurations (PBC in clustered landscape patterns that represent realistic future configurations or in dispersed neutral landscape models) on a nest abundance index in an Illinois landscape.
Results
Our modeling results suggest that crop composition and PBC area are particularly important for bee nest abundance, whereas landscape configuration is associated with bee nest abundance at the local scale but less so at the regional scale.
Conclusions
Strategies to enhance wild bee habitat should therefore emphasize the crop composition and amount of PBC.
Abscisic acid (ABA) is an essential hormone for plants to survive environmental stresses. At the center of the ABA signaling network is a subfamily of type 2C protein phosphatases (PP2Cs), which form exclusive interactions with ABA receptors and subfamily 2 Snfl-related kinase (SnRK2s). Here, we report a SnRK2-PP2C complex structure, which reveals marked similarity in PP2C recognition by SnRK2 and ABA receptors. In the complex, the kinase activation loop docks into the active site of PP2C, while the conserved ABA-sensing tryptophan of PP2C inserts into the kinase catalytic cleft, thus mimicking receptor-PP2C interactions. These structural results provide a simple mechanism that directly couples ABA binding to SnRK2 kinase activation and highlight a new paradigm of kinase-phosphatase regulation through mutual packing of their catalytic sites. 相似文献
It is believed that the different classes of compound which interfere with photosynthesis system II (PS 11) must act by binding at different sites, because they appear to be structurally so dissimilar. However, it can be argued that some of the classes of compound of diverse structural type share very similar external surface features. Now that details about the binding oj PSII inhibitors are becoming available, it will be possible to see how many of the different compound classes actually bind similarly. In future, increasingly detailed knowledge of the structures of potential sites of action will be available. QSAR methods will need to be used together with molecular modelling to be effective tools for agrochemical design. 相似文献
Seeds of perennial ryegrass Lolium perenne treated with four fungicides, benomyl, captan, iprodione and metalaxyl, used singly and in all combinations were sown in soil in pots. The soil was maintained at a low moisture content to predispose the seedlings to pre-emergence infection by soil-borne fungi. Thirteen of the fifteen fungicide treatments significantly increased seedling emergence and all but one contained benomyl and/or captan. In another pot experiment, a combination of benomyl and captan was tested against four similar treatments, carbendazim+captan, thiabendazole+captan, thiabendazole+metalaxyl and thiabendazole+thiram and also drazoxolon. Only benomyl+captan and drazoxolon did not increase seedling emergence significantly. A natural infection of the seedlings by powdery mildew Erysiphe graminis was reduced significantly by all treatments except thiabendazole+thiram and drazoxolon. Only car-bendazim+captan significantly increased the dry weight of seedlings per pot 98 days after sowing. Benomyl+captan seed treatment significantly increased seedling emergence in 9 of 16 soils collected from widespread sites. One perennial ryegrass cultivar, Parcour, was used in the above experiments and in a comparison with 12 other diploid cultivars its response to benomyl seed treatment was about mid-range. 相似文献
Agricultural, industrial and domestic use of surfactants leads to the entry of these compounds into terrestrial and aquatic ecosystems. Synthetic surfactants vary significantly in structure, but most consist of alkyl or alkylphenol groups attached to nonionic or anionic hydrophilic moieties. Continued use of these compounds is usually justified on the basis that they do not cause pollution problems because they undergo biodegradation by micro-organisms present in soils and surface waters. In accomplishing biodegradation, micro-organisms, predominantly bacteria, are exploiting these potentially useful resources of reduced carbon to derive energy and support growth in situations which are otherwise frequently oligotrophic. This paper reviews aspects of surfactant biodegradation, especially in relation to alcohol and alkylphenol ethoxylates used extensively as adjuvants for agrochemicals. In principle, bacteria can employ two strategies to gain access to the aliphatic chains in alcohol ethoxylate surfactants: separation of the hydrophobic chain from the hydrophile (central fission), or direct attack on the -terminal of the alkyl chain of the intact surfactant. Direct exo-cleavage of ethylene glycol units from the polyethylene glycol (PEG) chain also provides a third route to assimilable carbon. In pure cultures of known degraders or in mined environmental samples, all three strategies are exploited, some even within the same organism. Central fission occurs predominantly at the alkyl-ether bond, but may also occur within the PEG chain itself, thus producing various glycol intermediates which accumulate in pure cultures but appear only transiently in mixed environmental samples. Against this background, the relative resistance of some alkylphenol ethoxylates to biodegradation can be assessed in mechanistic terms. The steric bulk of the aryl nucleus effectively eliminates the central fission pathway. Moreover, some alkyl phenol ethoxylates contain branched alkyl chains which restrict ω-β-oxidation. As a result, ethoxylate shortening appears to be the major course of biodegradation observed so far. Not surprisingly, these surfactants are observed to undergo extensive primary biodegradation (removal of surfactant properties) but relatively restricted ultimate degradation to carbon dioxide and normal cell components. 相似文献