Integrating belowground carbon dynamics into Yield-SAFE,a parameter sparse agroforestry model

Agroforestry combines perennial woody elements (e.g. trees) with an agricultural understory (e.g. wheat, pasture) which can also potentially be used by a livestock component. In recent decades, modern agroforestry systems have been proposed at European level as land use alternatives for conventional agricultural systems. The potential range of benefits that modern agroforestry systems can provide includes farm product diversification (food and timber), soil and biodiversity conservation and carbon sequestration, both in woody biomass and the soil. Whilst typically these include benefits such as food and timber provision, potentially, there are benefits in the form of carbon sequestration, both in woody biomass and in the soil. Quantifying the effect of agroforestry systems on soil carbon is important because it is one means by which atmospheric carbon can be sequestered in order to reduce global warming. However, experimental systems that can combine the different alternative features of agroforestry systems are difficult to implement and long-term. For this reason, models are needed to explore these alternatives, in order to determine what benefits different combinations of trees and understory might provide in agroforestry systems. This paper describes the integration of the widely used soil carbon model RothC, a model simulating soil organic carbon turnover, into Yield-SAFE, a parameter sparse model to estimate aboveground biomass in agroforestry systems. The improvement of the Yield-SAFE model focused on the estimation of input plant material into soil (i.e. leaf fall and root mortality) while maintaining the original aspiration for a simple conceptualization of agroforestry modeling, but allowing to feed inputs to a soil carbon module based on RothC. Validation simulations show that the combined model gives predictions consistent with observed data for both SOC dynamics and tree leaf fall. Two case study systems are examined: a cork oak system in South Portugal and a poplar system in the UK, in current and future climate.     

Agroforestry for high value tree systems in Europe

Most farm-based agroforestry projects focus on the integration of trees on arable or livestock enterprises. This paper focuses on the integration of understorey crops and/or livestock within high value tree systems (e.g., apple orchards, olive groves, chestnut woodlands, and walnut plantations), and describes the components, structure, ecosystem services and economic value of ten case studies of this type of agroforestry across Europe. Although their ecological and socio-economic contexts vary, the systems share some common characteristics. The primary objective of the farmer is likely to remain the value of tree products like apples, olives, oranges, or nuts, or particularly high value timber. However there can still be production, environmental or economic benefits of integrating agricultural crops such as chickpeas and barley, or grazing an understorey grass crop with livestock. Three of the systems focused on the grazing of apple orchards with sheep in the UK and France. The introduction of sheep to apple orchards can minimise the need for mowing and provide an additional source of revenue. Throughout the Mediterranean, there is a need to improve the financial viability of olive groves. The case studies illustrate the possibility of intercropping traditional olive stands with chickpea in Greece, or the intercropping of wild asparagus in high density olive groves in Italy. Another system studied in Greece involves orange trees intercropped with chickpeas. Stands of chestnut trees in North-west Spain can provide feed for pigs when the fruit falls in November, and provide an excellent habitat for the commercial production of edible mushrooms. In Spain, in the production of high quality walnut trees using rotations of up to 50–60 years, there are options to establish a legume-based mixed pasture understorey and to introduce sheep to provide financial and environmental benefits.     

Phenotypic diversity among local Spanish and foreign peach and nectarine [Prunus persica (L.) Batsch] accessions

Phenotypic data for tree and fruit characteristics was collected over three consecutive years from a germplasm collection of 94 peach and nectarine accessions representing both traditional Spanish as well as foreign cultivars with widespread global plantings. All accessions were grown at the Experimental Station of Aula Dei located in the Ebro Valley (Northern Spain, Zaragoza) under a Mediterranean climate. Tree traits evaluated included bloom and harvest date, vigor, yield, yield efficiency and flower and leaf characteristics. Fruit traits included fresh weight, firmness, soluble solids, titratable acidity, levels of individual soluble sugars (sucrose, glucose, fructose and sorbitol), vitamin C, total phenolics, flavonoids, anthocyanins, relative antioxidant capacity and ripening index. Extensive variability was observed for most qualitative and quantitative traits with significant correlations identified between many traits. While the traditional Spanish accessions demonstrated good adaptability to the northern Spain evaluation site, opportunities for continued improvement in tree and fruit quality traits were demonstrated by an extensive phenotypic variability within the germplasm collection.     

Responses of rare and common segetal species to wheat competition and fertiliser type and dose

Fertiliser application is considered crucial for determining the crop–weed competition relationship by stimulating plant growth and modulating the competition for below‐ground (soil nutrients) and above‐ground resources (e.g. light and space). Segetal species, those preferentially inhabiting cereal fields, have suffered a strong decline, owing to agricultural intensification. Under continued pressure, particularly the rarest species may disappear. In this study, we aimed to assess the competitive ability of common and rare segetal species when growing with wheat and how this competitive relationship is modulated by the type (organic and mineral) and dose (low or high) of fertilisation in a pot experiment. The segetal species grew better at higher doses of fertilisers when growing alone. However, when growing with wheat, they were outcompeted by the cereal plants. Overall, flowering was not affected by the competition with wheat under the different fertiliser regimes. Only the onset of flowering of some segetal weeds tended to be delayed by crop competition. Some rare species were more affected by the competition with wheat, indicating that they may be disadvantaged in a community context. However, not all rare segetal species tested responded in the same way, which highlights that competitiveness alone is a poor predictor of the rarity of segetal species.     

Effect of temperature on RNA silencing of a negative‐stranded RNA plant virus: Citrus psorosis virus

Citrus psorosis virus (CPsV), genus Ophiovirus, causes a bark scaling disease of citrus. CPsV virions are kinked filaments with three negative‐stranded RNA molecules (vRNA) and a 48 kDa coat protein. The effect of temperature on symptom expression, virus accumulation and RNA silencing was examined in sweet orange seedlings (Citrus sinensis) graft‐inoculated with three different CPsV isolates and grown in a glasshouse at 26/18°C or 32/26°C (day/night). Most plants kept in the cooler glasshouse showed a shock reaction in the first flush with shoot necrosis, and then moderate to intense chlorotic flecking and spotting in young leaves, whereas plants incubated at 32/26°C did not exhibit shoot necrosis, and young leaf symptoms were milder. Virus titre estimated by ELISA and by northern and dot blot hybridization paralleled symptom intensity, with significantly higher virus accumulation in plants incubated at 26/18°C. The amount of CPsV‐derived small RNAs (CPsV‐sRNAs) slightly increased at 32/26°C, with the ratio of CPsV‐sRNA/vRNA being higher at 32/26°C than at 26/18°C. These results suggest that (i) CPsV infection induces RNA silencing in citrus plants, (ii) symptom intensity is associated with virus accumulation, and (iii) temperature increase enhances the RNA silencing response of citrus plants and decreases virus accumulation.     

ISSR markers detect high genetic variation among <Emphasis Type="Italic">Fusarium poae</Emphasis> isolates from Argentina and England

Fusarium poae is one of the Fusarium species isolated from cereal grains infected by Fusarium head blight (FHB), and in recent years it has been identified as a major FHB component. In this study, 97 F. poae isolates from Argentina (n = 62) and England (n = 35) were analysed by inter-simple sequence repeats (ISSR) to examine the genetic diversity and to determine whether intraspecific variation could be correlated with geographic and/or host origin. The molecular analysis showed high intraspecific variability within F. poae isolates, but did not reveal a clear relationship between variability and the host/geographic origin. Fusarium poae isolates from the same geographic region or host appeared in different subclusters. Conversely, isolates with the same haplotype were also collected from different geographic regions. However, we did observe subclusters consisting of isolates from Argentina only or from England only. Furthermore, a single seed sample was found to host different haplotypes. Analysis of molecular variance (AMOVA) indicated a high genetic variability in F. poae, with most of the genetic variability explained by differences within, rather than between Argentinean and English populations. This is the first report on genetic diversity of F. poae using ISSR markers. Moreover, ISSR fingerprinting generates highly polymorphic markers for F. poae and proved to be a useful and reliable assay for genetic variability studies.     

Plant‐available N:P alters root litter N recycling in a Mediterranean tree–grass ecosystem

Background: Nitrogen deposition can cause an ecosystem‐level shift in available N (nitrogen) to P (phosphorus) availability. However, most plant N nutrition is from edaphic sources rather than deposition and in seasonally dry grassland systems, root litter is the predominant nutrient source. Aims: We were interested how litter turnover and altered nutrient recycling from dead biomass can compensate for these shifts in ecosystem stoichiometry. Methods: We studied a Mediterranean savanna amended with N or NP treatments three years prior. We measured root and plant‐available soil N:P stoichiometry in two micro‐habitats: open pasture and beneath oak canopies. ¹⁵N‐labelled root litter incubated in topsoils without litterbags was used to trace uptake of litter N by herbaceous strata roots. Results: Since fertilization, NP added sites have become relatively P enriched, resulting in lower N:P ratios in living roots than either when N was added alone or control sites. Total litter‐derived ¹⁵N uptake by roots was proportional to root ingrowth response but higher in the NP than N treatment, indicating a higher N demand when N and P were added together. We observed more ¹⁵N uptake by plants under tree canopies, indicating a tighter nutrient recycling loop in these micro‐habitats in contrast to treatment level ‘fertility' trends. Conclusions: Root stoichiometry responded to manipulated soil nutrient availability and N uptake was altered as plants attempted to compensate for nutrient availability imbalances, indicating that these ecosystem perturbations have long term effects on nutrient cycling which can propagate to whole system function. This was also related to functional community‐level adaptions between micro‐habitats with under canopy communities more able to take advantage of the litter nutrient source.     

Analysis of the Relationship Between Submerged Aquatic Vegetation (SAV) and Water Trophic Status of Lakes Clustered in Northwestern Hillsborough County, Florida

This study examined the relationship between abundance of submerged aquatic vegetation (SAV) and the water trophic status of a group of lakes located in northwestern Hillsborough county. SAV abundance was expressed by the percent of lake volume infested with SAV (PVI) and the percent of lake area covered with SAV (PAC). The group of lakes was divided into two subgroups based on SAV abundance less than 20 PVI (PVI?<?20) and lakes with more than 20 PVI (PVI?>?20). Mean concentrations of total phosphorus (TP), total nitrogen (TN), and chlorophyll-?? in lake water were used as indicators of trophic status, with the concentration of each nutrient in one group of lakes compared to its corresponding concentration in the other group. Lakes with PVI?<?20 had a mean concentration of TP and chlorophyll-?? of 28 and 11 µg/l, respectively, while those with a PVI?>?20 had a mean concentration of 18 and 4 µg/l for the same parameters, respectively. The results of a t test and one-way ANOVA performed at the 95% confidence level indicated that the differences were significant for the concentrations of TP and chlorophyll-?? but not for TN, the last of which had a mean lake water concentration of 0.8 and 0.7 mg/l for the PVI?<?20 and PVI?>?20 subgroups, respectively.