This study aimed to understand the mechanisms of the variations in carbon (C) and nitrogen (N) pools and examine the possibility of differentiating the burning effects from seasonal and pre-existed N limitations in a native suburban forest ecosystem influenced by prescribed burning in subtropical Australia.
Materials and methods
Soil and litterfall samples were collected from two study sites from 1 to 23 months since last burnt. Soil labile C and N pools, soil C and N isotopic compositions (δ13C and δ15N), litterfall mass production (LM), and litterfall total C, total N, δ13C and δ15N were analysed. In-situ gas exchange measurements were also conducted during dry and wet seasons for Eucalyptus baileyana and E. planchoniana.
Results and discussion
The results indicated that labile C and N pools increased within the first few months after burning, with no correlations with climatic factors. Therefore, it was possible that the increase was due to the burning-induced factors such as the incorporation of ashes into the soil. The highest values of soil and litterfall δ15N, observed when the study was commenced at the experimental sites, and their high correlations with climatic factors were indicative of long-term N and water limitation. The 13C signals showed that soil N concentrations and climatic factors were also two of the main factors controlling litterfall and foliage properties mainly through the changes in photosynthetic capacity and stomatal conductance.
Conclusions
Long-term soil N availabilities and climatic factors were the two of the main driving factors of C and N cycling in the studied forest sites. Further studies are needed to compare soil and litterfall properties before and after burning to profoundly understand the effects of prescribed burning on soil labile C and N variations.
Due to a growing concern for black stem rust (BSR) disease in wheat-producing regions of the USA and Canada, the sale and movement of barberry plants to ‘quarantined’ regions is restricted to just a few cultivars approved as being BSR-resistant. Currently, verification of a given barberry plant as being ‘true-to-type’ of the approved cultivar relies on comparing its morphological features with those of its reference cultivar. Frequently, this approach leads to mis-identification of cultivars due to the similarity of morphological features among young plants. The approach is complicated, or not at all useful, when the plants are dormant, which is the stage at which plants are sold. A reliable technique that could be used at any stage of plant growth to identify and verify cultivars is needed. In this study, the genetic diversity of 51 barberry cultivars was assessed using microsatellite markers, and their genotypic profiles were developed based on the allele composition of different microsatellite loci. A total of 43 alleles were generated at seven microsatellite loci, and all were polymorphic. An unweighted pair group method with arithmetic averaging (UPGMA) cluster analysis of the Jaccard’s coefficient of similarity matrix showed that 84.3% of the 51 cultivars tested were distinct from each other. Ten of the 11 cultivars approved for import into Canada were distinguishable based on their genotypic profiles. The results indicated that microsatellite-based genotyping could be used by regulatory agencies to identify and offer ‘true-to-type’ guarantees to cultivars destined for BSR ‘quarantined’ regions, and to verify the uniqueness of new cultivars when issuing Plant Patents. 相似文献
This paper presents a review of the drainage development needs and prospects in developing countries and of the problems which need to be overcome. A distinction is made between the developments in the temperate, the (semi) arid zone and the (semi) humid zone. It is argued that the low level of attention given to drainage in the past may well have been justified in view of the low level of agricultural development, but, that in some of the more advanced developing countries, further agricultural development may stagnate if no timely investments in improved drainage are made. Improved drainage is also urgently required to arrest the land degradation and production loss caused by waterlogging and salinity in arid zone irrigated lands. Countries for which investment in drainage may not yet be opportune, would seem to be well advised to start building up some core institutional and professional capacity. The roles of government and of international development cooperation are also discussed. Finally, lessons learned and actions needed are identified. 相似文献
A polymerase chain reaction (PCR)-based test for potato late blight (Phytophthora infestans) and pink rot (P.erythroseptica, P. nicotianae) diseases has been developed for use with potato tuber tissue. Primers based on sequence analysis of the ITS2 region of ribosomal DNA of late blight and pink rot pathogens were utilized in PCR assays of inoculated tubers and tubers harvested from plots known to have late blight and/or pink rot. Assays of artificially inoculated Kennebec and Russet Burbank tubers revealed thatP. infestans was detected by PCR as early as 72 h after inoculation and in the absence of visible symptoms. Much higher detection frequencies were obtained by PCR compared with plating on selective medium or placement of tissue in moist chambers. Tubers from plots known to have late blight and/or pink rot were tested using the PCR assay. Assay of late blight lesions showed ca. 80% recovery for late blight-infected tubers from the field. Results indicate that the PCR assay provides a rapid and accurate test for diagnosis of late blight and pink rot in potato tubers. 相似文献
Changes in the fungal pathogenPhytophthora infestans in the United States pose a significant threat to potato production. Sources of resistance to these new genotypes of P.infestans need to be identified for potato breeders to have parental materials for crossing, and the phenotypic stability of late blight resistance in these potato clones needs to be determined. Sixteen potato clones which reportedly have some resistance to late blight were evaluated at eight locations: Florida (FL), Maine (ME), Michigan (MI), Minnesota (MN), North Dakota (ND), New York (NY), Pennsylvania (PA) and Wisconsin (WI) in 1996. Percent infected foliage was recorded at approximately weekly intervals following the onset of the disease at each location. Area under the disease progress curve (AUDPC) was calculated. Clones were ranked for mean AUDPC within location and the nonparametric stability statistics, mean absolute rank differences and variance of the ranks, were analyzed for phenotypic stability. Neither of these statistics was significant, indicating a lack of genotype x environment interaction on the rankings of these clones across locations in 1996. The four clones with lowest AUDPC scores were U.S. clones AWN86514-2, B0692-4, B0718-3 and B0767-2. These clones should be useful parental materials for breeders seeking to incorporate genes for late blight resistance into potatoes. 相似文献
Extrudate expansion of cereal‐based products is largely dependent on the molecular interactions and structural transformations that proteins undergo during extrusion processing. Such changes strongly influence the characteristic rheological properties of the melt. It is possible to modify rheological properties of wheat flour during extrusion processing, in particular shear viscosity, with cysteine. The objective of this work was to further develop an understanding of the molecular interactions and structural transformations of wheat flour from dynamic oscillatory rheological measurements. Temperature and frequency sweeps were conducted in the linear viscoelastic range of the material. Changes in the storage modulus (G′), the loss modulus (G″) and the loss tangent (tan δ) of 25% moisture wheat flour disks as a function of cysteine concentration (0–0.75%) were monitored. Molecular weight between cross‐links (Mc) and the number of cross‐links (Nc) per glutenin molecule were determined from frequency sweep data. Increasing cysteine concentration broke cross‐links by decreasing G′ maximum and increasing tan δ values. Molecular weight between cross‐links increased and the number of cross‐links decreased. G′ values from temperature sweeps showed a similar trend. This information leads to a better understanding of the viscoelastic behavior of wheat flour doughs during extrusion cooking and elucidation of protein‐protein reaction mechanisms and other interactions in extruded cereal‐based snack foods. 相似文献
Our research evaluates and compares the effects of three land‐related policies on land development in a sprawling metropolitan area during a real estate boom and a recession. Our findings suggest that during a real estate boom 1) the urban growth boundary (UGB) serves its purpose of attracting urban development inside the given boundary during a boom while its effectiveness diminishes with increased development pressure from lower‐valued land outside of the UGB during a recession period, 2) the agricultural zone works well for restraining new development during a boom period while agriculture zoned parcels are more likely developed during a recession period, and 3) an increase in the land‐value tax bill increases the incentive for development during a recession period while higher tax bills do not affect development during a boom period. In anticipation of a re‐emergence of urban sprawl with the recovery of the real estate market, our findings imply that land planners and others concerned with sprawling development should pay more attention to development in sprawl‐prone areas during recession periods. 相似文献