Prognosis of iron chlorosis in pear (Pyrus communis L.) and peach (Prunus persica L. Batsch) trees using bud, flower and leaf mineral concentrations

Background and Aims

The possibility of using tree materials in early phenological stages, such as dormant buds and flowers, for the prognosis of Fe deficiency occurring later in the year has been studied in peach and pear trees.

Methods

Thirty-two peach trees and thirty pear trees with different Fe chlorosis degrees were sampled in different commercial orchards. In peach, samples included flower buds, vegetative buds, bud wood, flowers and leaves at 60 and 120?days after full bloom (DAFB). In pear, samples included buds, bud wood, flowers and leaves at 60 and 120?days DAFB. Leaf chlorophyll was assessed (SPAD) at 60 and 120 DAFB. Sampling was repeated for 3–5?years depending on the materials. Mineral nutrients measured were N, P, K, Ca, Mg, Fe, Mn, Zn and Cu.

Results

The relationships between the nutrient concentrations in the different materials and leaf SPAD were assessed using four different statistical approaches: i) comparison of means depending on the chlorosis level, ii) correlation analysis, iii) principal component analysis, and iv) stepwise multiple regression. In all cases, significant associations between nutrients and SPAD were found. The best-fit multiple regression curves obtained for the multi-year data set provided good prediction in individual years.

Conclusions

Results found indicate that it is possible to carry out the prognosis of Fe chlorosis using early materials such as buds and flowers. The relationships obtained were different from those obtained in previous studies using a single orchard. The different methods of analysis used provided complementary data.     

Tree-microbial biomass competition for nutrients in a temperate deciduous forest,central Germany

Aims

Our goals were (1) to determine whether tree species diversity affects nutrient (N, P and K) cycling, and (2) to assess whether there is competition for these nutrients between microbial biomass and trees.

Methods

We measured nutrient resorption efficiency by trees, nutrient contents in leaf litterfall, decomposition rates of leaf litter, nutrient turnover in decomposing leaf litter, and plant-available nutrients in the soil in mono-species stands of beech, oak, hornbeam and lime and in mixed-species stands, each consisting of three of these species.

Results

Cycling of nutrients through leaf litter input and decomposition were influenced by the types of tree species and not simply by tree species diversity. Trees and microbial biomass were competing strongly for P, less for K and only marginally for N. Such competition was most pronounced in mono-species stands of beech and oak, which had low nutrient turnover in their slow decomposing leaf litter, and less in mono-species stands of hornbeam and lime, which had high nutrient turnover in their fast decomposing leaf litter.

Conclusions

The low soil P and K availability in beech stands, which limit the growth of beech at Hainich, Germany, were alleviated by mixing beech with hornbeam and lime. These species-specific effects on nutrient cycling and soil nutrient availability can aid forest management in improving productivity and soil fertility.

     

Spatial patterns of total and available N and P at alpine treeline

Background and aims

Vegetation can have direct and indirect effects on soil nutrients. To test the effects of trees on soils, we examined the patterns of soil nutrients and nutrient ratios at two spatial scales: at sites spanning the alpine tundra/subalpine forest ecotone (ecotone scale), and beneath and beyond individual tree canopies within the transitional krummholz zone (tree scale).

Methods

Soils were collected and analyzed for total carbon (C), nitrogen (N), and phosphorus (P) as well as available N and P on Niwot Ridge in the Colorado Rocky Mountains.

Results

Total C, N, and P were higher in the krummholz zone than the forest or tundra. Available P was also greatest in the krummholz zone while available N increased from the forest to the tundra. Throughout the krummholz zone, total soil nutrients and available P were higher downwind compared to upwind of trees.

Conclusions

The krummholz zone in general, and downwind of krummholz trees in particular, are zones of nutrient accumulation. This pattern indicates that the indirect effects of trees on soils are more important than the direct effects. The higher N:P ratios in the tundra suggest nutrient dynamics differ from the lower elevation sites. We propose that evaluating soil N and P simultaneously in soils may provide a robust assay of ecosystem nutrient limitation.     

Prediction of leaf nitrogen from early season samples and development of field sampling protocols for nitrogen management in Almond (Prunus dulcis [Mill.] DA Webb)

Background and aim

Protocols for leaf sampling in deciduous tree crops are commonly executed too late in the season and do not adequately consider field variability to be effectively used to guide N management. The goal of this study was to develop improved sampling strategies to optimize nitrogen management in deciduous tree crops.

Method

Leaf nutrient concentration from individual trees in four mature commercial orchards was collected (n =1148) for three consecutive seasons to develop nitrogen prediction models and to estimate the distribution of N values in orchards in July. Spatial variance analysis was used to determine optimal sampling strategies.

Results

Leaf nitrogen concentration in summer can be predicted (r²?=?0.9) from the leaf N and B concentration in spring with the sum of K, Ca, and Mg equivalents. Mean field leaf nutrient concentration can be obtained by collecting one pooled sample per management zone composed of 30 trees each of which are at least 30 m apart. Using these methods the percentage of trees with leaf N above the recommended July critical value can be predicted accurately.

Conclusions

Optimized methods for sample collection and models to predict mid-season leaf N from early season samples can be used to improve N management in deciduous tree crops.     

Can savannas become forests? A coupled analysis of nutrient stocks and fire thresholds in central Brazil

Aims

The effects of fire ensure that large areas of the seasonal tropics are maintained as savannas. The advance of forests into these areas depends on shifts in species composition and the presence of sufficient nutrients. Predicting such transitions, however, is difficult due to a poor understanding of the nutrient stocks required for different combinations of species to resist and suppress fires.

Methods

We compare the amounts of nutrients required by congeneric savanna and forest trees to reach two thresholds of establishment and maintenance: that of fire resistance, after which individual trees are large enough to survive fires, and that of fire suppression, after which the collective tree canopy is dense enough to minimize understory growth, thereby arresting the spread of fire. We further calculate the arboreal and soil nutrient stocks of savannas, to determine if these are sufficient to support the expansion of forests following initial establishment.

Results

Forest species require a larger nutrient supply to resist fires than savanna species, which are better able to reach a fire-resistant size under nutrient limitation. However, forest species require a lower nutrient supply to attain closed canopies and suppress fires; therefore, the ingression of forest trees into savannas facilitates the transition to forest. Savannas have sufficient N, K, and Mg, but require additional P and Ca to build high-biomass forests and allow full forest expansion following establishment.

Conclusions

Tradeoffs between nutrient requirements and adaptations to fire reinforce savanna and forest as alternate stable states, explaining the long-term persistence of vegetation mosaics in the seasonal tropics. Low-fertility limits the advance of forests into savannas, but the ingression of forest species favors the formation of non-flammable states, increasing fertility and promoting forest expansion.     

Nutrient stocks in litterfall and litter in cocoa agroforests in Brazil

Aim

To compare the internal balances of nutrients and the rates of nutrient cycling across nine cocoa agroforestry systems consisting of various combination of soil types (Latosols and Cambisols), production systems (cabruca and Erythrina glauca-shade) and fertilization regimes in southern Bahia, Brazil.

Methods

We measured nutrient stocks in litter fall production, in the accumulated litter and fruits. The internal nutrient balance for various simulations was obtained by the following expressions: (1) Balance 1?=?litter – fruit (seeds and husks) and (2) Balance 2?=?(litter?+?husks) – seeds. Annual litter decomposition coefficients (k) and subsequent potential of nutrient release were also investigated. The data were analyzed by principal components analysis and by Pearson correlations.

Results

There was a high degree of dissimilarity among the cocoa agrosystems in relation to the nutrient cycling and the internal nutrient balance. The mean annual litterfall production ranged from 4.6 to 8.5 Mg/ha, and the amount of accumulated litter ranged from 7.7 to 16.8 Mg/ha. The results showed significant differences in quality among litter from cocoa agroforests; the decomposition coefficient of litter and the subsequent nutrient release were regulated by the litter quality. In general, the cocoa-erythrina system presented a higher capacity to recycle nutrients compared to the cocoa-cabruca system, with the cocoa-erythrina system having the largest transfer rate of nutrients through litterfall, high values for the decomposition coefficient of litter and the lowest values for the Mean Residence Time of nutrients. Cocoa tree leaves functioned as a sink of nutrients, while shade tree leaves functioned predominantly as a source. The nutritional reserves of litter?+?cocoa fruit husks, with respect only to the nutrients exported in the seeds, the balance was positive for all nutrients (N, P, K, Ca and Mg) in all agroforests, which emphasizes the potential productive capacity of these agroforests to sustain the estimated production in different harvest cycles.

Conclusions

The internal balance of nutrients reflects an agroforests’s productive capacity, which accumulated litter and cocoa fruit husks may be important nutrient sources that could enable the development of fertilizer recommendation systems aimed at increasing the efficiency of fertilizer use and at maintaining soil fertility in cocoa agroforests. Therefore, further research is needed to develop nutritional balance systems integrating litter?+?fruits stock and other nutrient pathways (e.g., soil quality, biological N fixation, leaching), which were not measured, for making recommendations regarding liming and fertilizers that are suitable for highly complex biological agrosystems, such as cocoa agroforests that have low levels of elements exported during seed production.     

LabKey Server: An open source platform for scientific data integration, analysis and collaboration

Background

This paper is devoted to distance measures for leaf-labelled trees on free leafset. A leaf-labelled tree is a data structure which is a special type of a tree where only leaves (terminal) nodes are labelled. This data structure is used in bioinformatics for modelling of evolution history of genes and species and also in linguistics for modelling of languages evolution history. Many domain specific problems occur and need to be solved with help of tree postprocessing techniques such as distance measures.

Results

Here we introduce the tree edit distance designed for leaf labelled trees on free leafset, which occurs to be a metric. It is presented together with tree edit consensus tree notion. We provide statistical evaluation of provided measure with respect to R-F, MAST and frequent subsplit based dissimilarity measures as the reference measures.

Conclusions

The tree edit distance was proven to be a metric and has the advantage of using different costs for contraction and pruning, therefore their properties can be tuned depending on the needs of the user. Two of the presented methods carry the most interesting properties. E(3,1) is very discriminative (having a wide range of values) and has a very regular distance distribution which is similar to a normal distribution in its shape and is good both for similar and non-similar trees. NFC(2,1) on the other hand is proportional or nearly proportional to the number of mutation operations used, irrespective of their type.     

Soil nutrient patchiness and plant genotypes interact on the production potential and decomposition of root and shoot litter: evidence from short-term laboratory experiments with Triticum aestivum

Aims

The purpose of this study was to test the hypotheses that soil nutrient patchiness can differentially benefit the decomposition of root and shoot litters and that this facilitation depends on plant genotypes.

Methods

We grew 15 cultivars (i.e. genotypes) of winter wheat (Triticum aestivum L.) under uniform and patchy soil nutrients, and contrasted their biomass and the subsequent mass, carbon (C) and nitrogen (N) dynamics of their root and shoot litters.

Results

Under equal amounts of nutrients, patchy distribution increased root biomass and had no effects on shoot biomass and C:N ratios of roots and shoots. Roots and shoots decomposed more rapidly in patchy nutrients than in uniform nutrients, and reductions in root and shoot C:N ratios with decomposition were greater in patchy nutrients than uniform nutrients. Soil nutrient patchiness facilitated shoot decomposition more than root decomposition. The changes in C:N ratios with decomposition were correlated with initial C:N ratios of litter, regardless of roots or shoots. Litter potential yield, quality and decomposition were also affected by T. aestivum cultivars and their interactions with nutrient patchiness.

Conclusions

Soil nutrient patchiness can enhance C and N cycling and this effect depends strongly on genotypes of T. aestivum. Soil nutrient heterogeneity in plant communities also can enhance diversity in litter decomposition and associated biochemical and biological dynamics in the soil.     

Competitive interaction between the exotic plant Rhus typhina L. and the native tree Quercus acutissima Carr. in Northern China under different soil N:P ratios

Background and aims

Anthropogenic nitrogen (N) and phosphorus (P) input has changed the relative importance of nutrient elements. This study aimed to examine the effects of different nutrient conditions on the interaction between exotic and native plants.

Methods

We conducted a greenhouse experiment with a native species Quercus acutissima Carr. and an exotic species Rhus typhina L. grown in monocultures or mixtures, under three N:P ratios (5, 15 and 45 corresponding to N-limited, basic N and P supply and P-limited conditions, respectively). After 12 weeks of treatment, traits related to biomass allocation, leaf physiology and nutrient absorption were determined.

Results

R. typhina was dominant under competition, with a high capacity for carbon assimilation and nutrient absorption, and the dominance was unaffected by increasing N:P ratios. R. typhina invested more photosynthate in leaves and more nutrients in the photosynthetic apparatus, enabling high biomass production. Q. acutissima invested more photosynthate in roots and more nutrients in leaf persistence at the expense of reduced carbon assimilation capacity.

Conclusions

Different trade-offs in biomass and nutrient allocation of the two species is an important reason for their distinct performances under competition and helps R. typhina to maintain dominance under different nutrient conditions.     

Soil organic C and nutrient contents under trees with different functional characteristics in seasonally dry tropical silvopastures

Aims

The selection of tree characteristics is critical for the outcome of the tree effects on soil fertility in silvopastoral pastures. This study aims to quantify the effects of trees on soil nutrient and C stocks, as well as assessing differences on the effects between legume (Albizia saman; Enterolobium cyclocarpum) and non-legume tree species (Tabebuia rosea; Guazuma ulmifolia).

Methods

In Central Nicaragua, soil was sampled (0–10 cm deep) in paired plots, under both a canopy and in open grassland, in 12 sites per tree species and analysed for organic C, total N stocks, available P and extractable K⁺, Ca²⁺ and Mg²⁺. To assess the effects of herbaceous composition and cattle to soil proprieties, we recorded the cover of plant groups and assessed the mass of dung in each plot.

Results

Soil organic C and N, available P and extractable K⁺ and Ca²⁺ were higher under the tree canopy than under paired open grassland. The basal area of trees was positively related with the canopy effect on soil variables, thus suggesting that the age or sizes of the trees are relevant factors associated with the content of soil C and nutrients. No specific effects related to the legume species group were detected.

Conclusions

Our results indicate that in fertile seasonally dry subtropical pastures, scattered trees have an overall effect on soil fertility, and that the magnitude of the effect depends more on the tree characteristics (i.e. basal area, crown area) than on whether the species is a legume or not.     

Pinyon pine (Pinus edulis) mortality and response to water addition across a three million year substrate age gradient in northern Arizona, USA

Background and aims

Pinyon pine (Pinus edulis Engelm.) is an important tree species in the western United States that has experienced large-scale mortality during recent severe drought. The influence of soil conditions on pinyon pine response to water availability is poorly understood. We investigated patterns of tree mortality and response of tree water relations and growth to experimental water addition at four sites across a three million year soil-substrate age gradient.

Methods

We measured recent pinyon mortality at four sites, and tree predawn water potential, leaf carbon isotope signature, and branch, leaf, and stem radial growth on 12 watered and unwatered trees at each site. Watered trees recieved fifty percent more than growing season precipitation for 6 years.

Results

Substrate age generally had a greater effect on tree water stress and growth than water additions. Pinyon mortality was higher on intermediate-aged substrates (50–55%) than on young (15%) and old (17%) substrates, and mortality was positively correlated with pinyon abundance prior to drought.

Conclusions

These results suggest high soil resource availability and consequent high stand densities at intermediate-age substrates predisposes trees to drought-induced mortality in semi-arid regions. The response of tree water relations to water addition was consistent with the inverse texture hypothesis; watering reduced tree water stress most in young, coarsely textured soil, likely because water rapidly penetrated deep in the soil profile where it was protected from evapotranspiration.     

Savanna soil fertility limits growth but not survival of tropical forest tree seedlings

Background and Aims

Cerradão (Brazilian woodland savannas) and seasonally dry forests (SDF) from southeastern Brazil occur under the same climate but are remarkably distinct in species composition. The objective of this study was to evaluate the role of soil origin in the initial growth and distribution of SDF and Cerradão species.

Methods

We conducted a greenhouse experiment growing Cerradão and SDF tree seedlings over their soil and the soil of the contrasting vegetation type. We evaluated soil nutrient availability and seedling survivorship, growth and leaf functional traits.

Results

Despite the higher nutrient availability in SDF soils, soil origin did not affect seedling survivorship. The three SDF species demonstrated home-soil advantage, enhanced growth with increasing soil nutrient availability and had higher growth rates than Cerradão species, even on Cerradão soils. Growth of Cerradão seedlings was not higher on Cerradão soil and, overall, was not positively correlated with soil nutrient availability.

Conclusions

SDF species are fast-growing species while Cerradão trees tend to be slow-growing species. Although savanna soil reduces growth of forest species, our findings suggest that soil chemical attributes, alone, does not exclude the occurrence of SDF seedlings in Cerradão and vice-versa.     

Influence of potassium and sodium nutrition on leaf area components in Eucalyptus grandis trees

Background and Aims

Recent studies showed a positive tree response to Na addition in K-depleted tropical soils. Our study aimed to gain insight into the effects of K and Na fertilizations on leaf area components for a widely planted tree species.

Methods

Leaf expansion rates, as well as nutrient, polyol and soluble sugar concentrations, were measured from emergence to abscission of tagged leaves in 1-year-old Eucalyptus grandis plantations. Leaf cell size and water status parameters were compared 1 and 2 months after leaf emergence in plots with KCl application (+K), NaCl application (+Na) and control plots (C).

Results

K and Na applications enhanced tree leaf area by increasing both leaf longevity and the mean area of individual leaves. Higher cell turgor in treatments +K and +Na than in the C treatment resulting from higher concentrations of osmotica contributed to increasing both palisade cell diameters and the size of fully expanded leaves.

Conclusions

Intermediate total tree leaf area in treatment +Na compared to treatments C and +K might result from the capacity of Na to substitute K in osmoregulatory functions, whereas it seemed unable to accomplish other important K functions that contribute to delaying leaf senescence.     

Stem growth and phenology of two tropical trees in contrasting soil conditions

Background and aims

Phenological variations in tropical forests are usually explained by climate. Nevertheless, considering that soil water availability and nutrient content also influence plant water status and metabolism, soil conditions may also be important in the regulation of plant reproductive and vegetative activities over time. We investigated whether phenological patterns and stem growth differ in trees growing in two types of soil that display contrasting water and nutrient availability, namely, Gleysol (moist and nutrient-poor) and Cambisol (drier and nutrient-rich).

Methods

Phenological observations (flushing, leaf fall, flowering and fruiting) and stem diameter growth were recorded for 120 trees fitted with fixed dendrometer bands, at 15 days intervals, for 1 year. Two species of contrasting deciduousness were investigated: Senna multijuga (semi-deciduous) and Citharexylum myrianthum (deciduous).

Results

Both species were seasonal in all phenophases, regardless of soil type. However, frequency, mean date and intensity of phenophases varied according to soil type. Girth increment of C. myrianthum was four times greater in Cambisol than in Gleysol, whereas the type of soil had no significant effect on that of S. multijuga.

Conclusions

These results show that soil characteristics also play an important role in determining phenological patterns and growth and must be considered when analysing phenological patterns in tropical forests.     

Effects on nutrient cycling of conifer restoration in a degraded tropical montane forest

Background and aims

Exotic coniferous species have been used widely in restoration efforts in tropical montane forests due to their tolerance to adverse conditions and rapid growth, with little consideration given to the potential ecological benefits provided by native tree species. The aim of this study was to elucidate differences in litterfall and nutrient flow between a montane oak forest (Quercus humboldtii Bonpl.) and exotic coniferous plantations of pine (Pinus patula Schltdl. & Cham.) and cypress (Cupressus lusitanica Mill.) in the Colombian Andes.

Methods

Litter production, litter decomposition rate, and element composition of leaf litter were monitored during 3 years.

Results

Litter production in the oak forest and pine plantation was similar, but considerably lower in the cypress plantation . Similar patterns were observed for nutrient concentrations in litterfall, with the exception of Ca which was three times higher in the cypress plantation. The annual decay rate of litter was faster in the montane oak forest than in either of the exotic coniferous plantations. The potential and net return of nutrients to the forest floor were significantly higher in oak forest than in the exotic coniferous plantations.

Conclusions

Future restoration programs should consider new species that can emulate the nutrient flow of native broadleaf species instead of exotic species that tend to impoverish soil nutrient stocks in tropical montane forests.     

Relationships between leaf morphological traits, nutrient concentrations and isotopic signatures for Mediterranean woody plant species and communities

Background and aims

Soil factors are driving forces that influence spatial distribution and functional traits of plant species. We test whether two anchor morphological traits—leaf mass per area (LMA) and leaf dry matter content (LDMC)—are significantly related to a broad range of leaf nutrient concentrations in Mediterranean woody plant species. We also explore the main environmental filters (light availability, soil moisture and soil nutrients) that determine the patterns of these functional traits in a forest stand.

Methods

Four morphological and 19 chemical leaf traits (macronutrients and trace elements and δ¹³C and δ¹⁵N signatures) were analysed in 17 woody plant species. Community-weighted leaf traits were calculated for 57 plots within the forest. Links between LMA, LDMC and other leaf traits were analysed at the species and the community level using standardised major axis (SMA) regressions

Results

LMA and LDMC were significantly related to many leaf nutrient concentrations, but only when using abundance-weighted values at community level. Among-traits links were much weaker for the cross-species analysis. Nitrogen isotopic signatures were useful to understand different resource-use strategies. Community-weighted LMA and LDMC were negatively related to light availability, contrary to what was expected.

Conclusion

Community leaf traits have parallel shifts along the environmental factors that determine the community assembly, even though they are weakly related across individual taxa. Light availability is the main environmental factor determining this convergence of the community leaf traits.     

How does winter pruning affect peach tree–Myzus persicae interactions?

Winter tree pruning is a cultural practice known to modify vegetative growth, which is likely to affect the development of pests. However, it has been poorly addressed as a cultural control method for diminishing the population levels of the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae), in peach [ Prunus persica (L.) Batsch (Rosaceae)] orchards. In this study, we conducted a 2-year, on-station experiment to evaluate how winter pruning affects peach– M. persicae interactions, by examining tree vegetative growth, aphid population dynamics, and crop yield and fruit quality. We collected data under an insect-proof shelter on adult peach trees submitted to various levels of pruning and artificially infested with aphids. Our results showed that pruning enhanced shoot growth due to the proportion of growing shoots, which increased exponentially (10–60%), whereas the growth rate of growing shoots was not affected. The degree of infestation of peach trees increased with increasing pruning intensity. This effect was mainly due to the increase of the proportion of growing shoots, on which aphids developed better than on rosettes. In turn, the higher the aphid infestation, the higher the aphid-induced shoot-tip damage, leaf curling, and leaf fall that disturbed the growth of growing shoots. However, aphids did not considerably reduce fruit quality at harvest. They did not affect fresh fruit weight, and the refractometric index (indicator of sugar content) was reduced by only 3–4%. The relevance of winter pruning as a cultural method for pest control in orchards conducted under integrated fruit production guidelines is discussed.     

Tree development in structural soil – an empirical below-ground in-situ study of urban trees in Copenhagen,Denmark

Aims

The purpose of this study is to evaluate root and stem growth, nutrient status and soil properties of a tree planting in structural soil.

Methods

Root and stem growth were measured at an 10-year-old urban planting of Tilia x europaea L. ‘Pallida’ established in structural soil on a paved square in Copenhagen, Denmark.Root abundance was quantified and soil profiles were established at three different distances from 10 trees (1.0, 1.9, and 2.9 m). Soil and leaf samples were analysed for nutrient concentrations.

Results

Abundant root presence was measured across the entire profile of structural soil (160?×?60 cm) at all distances, provided that structural soil layers were constructed correctly. Erroneously constructed structural soil layers however, resulted in impaired tree and root growth. Coarse root morphology was affected by the confined growing space in the voids of the stone matrix. The soil was relatively alkaline with an average pH (CaCl₂) of 7.3. Foliar analysis revealed deficiencies of K and Mn. These deficiencies might be due to a combined effect of high pH and low soil concentrations of these nutrients.

Conclusions

The study documents that correctly constructed structural soils allow and encourage root growth in load bearing layers.

     

Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach

Key message

The paper identifies and quantifies how crop load influences plant physiological variables that determine stem diameter variations to better understand the effect of crop load on drought stress indicators.

Abstract

Stem diameter (D ^stem) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two D ^stem derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages.     

Photosynthetic responses to soil water stress in summer in two Japanese urban landscape tree species (<Emphasis Type="Italic">Ginkgo biloba</Emphasis> and <Emphasis Type="Italic">Prunus yedoensis</Emphasis>): effects of pruning mulch and irrigation management

Key message

Stomatal regulation involves beneficial effects of pruning mulch and irrigation on leaf photosynthesis in Prunus yedoensis and Ginkgo biloba under moderate drought. G. biloba showed conservative water use under drought.

Abstract

Leaf photosynthesis is highly sensitive to soil water stress via stomatal and/or biochemical responses, which markedly suppress the growth of landscape trees. Effective irrigation management to maintain leaf photosynthesis and information on species-specific photosynthetic responses to soil water stress are essential for the sustainable management of landscape trees in Japan, in which summer drought often occurs. In order to investigate effective irrigation management, we used plants with moderate soil water stress as controls, and examined the effects of daily irrigation and pruning mulch on leaf photosynthesis in container-grown Ginkgo biloba and Prunus yedoensis, which are the first and second main tall roadside trees in Japan. Stomatal conductance was significantly increased by pruning mulch and daily irrigation, with similar increases in leaf photosynthesis being observed in P. yedoensis and G. biloba. In order to obtain information on species-specific photosynthetic responses to soil water stress, we compared the responses of leaf photosynthesis and leaf water status to reductions in soil water content (SWC) between the two species. G. biloba maintained a constant leaf water potential, leaf water content, maximum carboxylation rate, and electron transport rate with reductions in SWC, whereas reductions were observed in P. yedoensis. We concluded that pruning mulch and irrigation effectively offset the negative impact of moderate water stress on leaf photosynthesis in summer in P. yedoensis and G. biloba via stomatal regulation, and also that G. biloba maintained its photosynthetic biochemistry and leaf water status better than P. yedoensis under severe water stress.