We estimated the proportions of anadromous and freshwater‐resident brown trout (Salmo trutta) in different parts of the subarctic River Näätämöjoki/Neidenelva system (Finland and Norway) using carbon, nitrogen and hydrogen stable isotope analyses of archived scales as identifiers of migration strategy. Our results showed that carbon stable isotope values were the best predictor of migration strategy. Most individuals fell into two clearly distinct groups representing anadromous (47%) or freshwater‐resident (42%) individuals, but some fish had intermediate carbon values suggesting repeated movement between freshwater and the sea. The proportion of anadromous individuals decreased steadily with distance from the sea forming a spatial continuum in migration strategies which is probably maintained by the combination of several factors such as divergent availability of food resources, variable migration costs and genetic differences. These within‐catchment differences in migration strategies should be taken into account in fisheries management practices. 相似文献
AbstractSince its emergence in Africa in 2016, fall armyworm (FAW) has spread rapidly and poses a severe threat to the food security and livelihood of millions of smallholder farmers in the continent. Using survey data from Ghana and Zambia, we examined FAW prevention and control methods implemented by farm households and their impacts on maize output and household consumption of self-produced maize. The main control methods used included pesticide application and handpicking of larvae, while access to information on FAW was a key driver behind the implementation of the control methods. Results from an endogenous switching regression showed that the implementation of a FAW management strategy significantly enhanced maize yield and households’ own maize consumption. When disentangling the impacts of the main control methods, we found that the combination of pesticide application and handpicking of larvae produced the highest yield gain of 125%. We concluded that the current interventions put in place by farmers to tackle FAW infestations are providing positive outcomes, but successful management of the pest will require more actions, including raising awareness to enhance the adoption of control interventions and exploring other control options. 相似文献
Trees exposed to elevated CO2 partial pressure ([CO2]) generally show increased rates of photosynthesis and growth, but effects on leaf respiration are more variable. The causes of this variable response are unresolved. We grew 12-year-old sweetgum trees (Liquidambar styraciflua L.) in a Free-Air CO2 Enrichment (FACE) facility in ambient [CO2] (37/44 Pa daytime/nighttime) and elevated [CO2] (57/65 Pa daytime/nighttime) in native soil at Oak Ridge National Environmental Research Park. Nighttime respiration (R(N)) was measured on leaves in the upper and lower canopy in the second (1999) and third (2000) growing seasons of CO2 fumigation. Leaf respiration in the light (R(L)) was estimated by the technique of Brooks and Farquhar (1985) in the upper canopy during the third growing season. There were no significant short-term effects of elevated [CO2] on R(N) or long-term effects on R(N) or R(L), when expressed on an area, mass or nitrogen (N) basis. Upper-canopy leaves had 54% higher R(N) (area basis) than lower-canopy leaves, but this relationship was unaffected by CO2 growth treatment. In August 2000, R(L) was about 40% of R(N) in the upper canopy. Elevated [CO(2)] significantly increased the number of leaf mitochondria (62%), leaf mass per unit area (LMA; 9%), and leaf starch (31%) compared with leaves in ambient [CO(2)]. Upper-canopy leaves had a significantly higher number of mitochondria (73%), N (53%), LMA (38%), sugar (117%) and starch (23%) than lower-canopy leaves. Growth in elevated [CO2] did not affect the relationships (i.e., intercept and slope) between R(N) and the measured leaf characteristics. Although no factor explained more than 45% of the variation in R(N), leaf N and LMA were the best predictors for R(N). Therefore, the response of RN to CO2 treatment and canopy position was largely dependent on the magnitude of the effect of elevated [CO2] or canopy position on these characteristics. Because elevated [CO2] had little or no effect on N or LMA, there was no effect on R(N). Canopy position had large effects on these leaf characteristics, however, such that upper-canopy leaves exhibited higher R(N) than lower-canopy leaves. We conclude that elevated [CO2] does not directly impact leaf respiration in sweetgum and that barring changes in leaf nitrogen or leaf chemical composition, long-term effects of elevated [CO2] on respiration in this species will be minimal. 相似文献
Evaluation of existing on-farm agroforestry plots should provide useful supplementary information for the design of improved agroforestry systems, in both research and development projects. Such evaluation has been little used, however, largely due to the methodological difficulties of surveying highly variable on-farm plots, and difficulties in identifying key variables for measurement. This paper describes a set of methods and tools used in evaluating plots of alley-cropping and tree borders around crop fields established by farmers working with the CARE Agroforestry Extension Project in western Kenya. Details of survey design, sampling, and implementation are discussed, and suggestions made for carrying out agroforestry surveys in other projects. A condensed version of the questionnaire is appended. 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
Within-leaf variations in cell size, mitochondrial numbers and dark respiration rates were compared in the most recently expanded tip, the mid-section and base of needles of Pinus radiata D. Don trees grown for 4 years in open-top chambers at ambient (36 Pa) or elevated (65 Pa) carbon dioxide partial pressure (p(CO2)a). Mitochondrial numbers and respiratory activity varied along the length of the needle, with the highest number of mitochondria per unit cytoplasm and the highest rate of respiration per unit leaf area at the base of the needle. Regardless of the location of the cells (tip, middle or basal sections), needles collected from trees grown in elevated p(CO2)a had nearly twice the number of mitochondria per unit cytoplasm as those grown in ambient p(CO2)a. This stimulation of mitochondrial density by growth at elevated p(CO2)a was greater at the tip of the needle (2.7 times more mitochondria than in needles grown in ambient CO2) than at the base of the needle (1.7 times). The mean size of individual mitochondria was unaffected either by growth at elevated p(CO2)a or by position along the needle. Tree growth at elevated p(CO2)a had a variable effect on respiration per unit leaf area, significantly increasing respiration in the tip of the needles (+25%) and decreasing respiration at the mid-section and base of the needles (-14% and -25%, respectively). Although a simple relationship between respiration per unit leaf area and mitochondrial number per unit cytoplasm was found within each CO2 treatment, the variable effect of growth at elevated p(CO2)a on respiration along the length of the needles indicates that a more complex relationship must determine the association between structure and function in these needles. 相似文献