Elemental and stable isotope composition of Pinus halepensis foliage along a metal(loid) polluted gradient: implications for phytomanagement of mine tailings in semiarid areas

Background and aims

Aleppo pine (Pinus halepensis Mill.) is a widely used species for restoring degraded semiarid areas, but its use for the revegetation of metal(loid) polluted soils has not been thoroughly investigated. The main goal of this research was to study the ecophysiological status and elemental composition of spontaneous populations of Pinus halepensis growing on mine tailings to assess their use in phytomanagement of mine spoils in semiarid climates.

Methods

Edaphic characteristics and the physiological (by stable isotopes) and nutritional status of pine trees were determined on mine tailings, in the metalloid-polluted surroundings and a non-polluted control area.

Results

Low soil phosphorus availability at the tailings was found to be a more important limiting factor for pine physiological performance than high soil metal(lloid)s concentrations. Foliar phosphorus concentrations showed a strong negative correlation with foliar sulphur concentrations along the studied transect. The carbon and oxygen isotopic composition (δ¹³C and δ¹⁸O) of pine needles indicated that trees at the tailings were less water stressed than those in surroundings or control areas. The low foliar δ¹⁵N of pines growing at the tailings was due to low soil fertility and/or a heavy reliance on symbiotic ectomycorrhizal fungi for nitrogen uptake.

Conclusions

The results of this study indicate that Pinus halepensis is a suitable tree species for the phytostablisation of neutral or slightly-alkaline mining wastes in semiarid environments, thanks to its drought hardiness and good adaptation to low soil fertility and salinity.     

Overstorey and juvenile response to thinning and drought in a jarrah (Eucalyptus marginata Donn ex Sm.) forest of southwestern Australia

Aims

Forest thinning is expected to affect tree water use and carbon assimilation, but the related influence from climate variability is little known. Recent forest thinning in the Wungong catchment coincided with a record dry year following the thinning, which provides a rare opportunity to understand the climate influence on the thinning effect.

Methods

A field experiment was conducted to examine changes before and after thinning, especially the rainfall, soil moisture, leaf water status, tissue isotope signature (¹³?C and ¹⁵?N) and N concentration of overstorey and understorey juvenile trees of Eucalyptus marginata (Donn ex Sm.).

Results

Despite the post-thinning drought, surface soil was moister and juvenile jarrah plants were less water stressed, attributable to reduced rain interception and transpiration as a result of less canopy cover. The overstorey was under stress but mainly due to drought rather than by thinning. The concentration of N declined in both tree stems and juvenile leaves along with available N in soil, suggesting a soil N limitation. No treatment effects were detected from leaf relative water content and tissue isotope signature (¹³?C and ¹⁵?N).

Conclusions

The drought effects were superimposed over the thinning effects on overstorey growth, with stemwood δ¹³C being a major indicator of water stress. The water relations and carbon assimilation of understorey juveniles were however dependent more on topsoil moisture, and the wetter soil during the year following thinning enhanced growth activity and hence the depletion of ¹³?C (more negative δ¹³C) in juvenile leaves.     

Effectiveness of soil N availability indices in predicting site productivity in the oil sands region of Alberta

Background and aims

Quantitative relationships between soil N availability indices and tree growth are lacking in the oil sands region of Alberta and this can hinder the development of guidelines for the reclamation of the disturbed landscape after oil sands extraction. The aim of this paper was to establish quantitative relationships between soil N availability indices and tree growth in the oil sands region of Alberta.

Methods

In situ N mineralization rates, in situ N availability measured in the field using Plant Root Simulators (PRS? probes), laboratory aerobic and anaerobic soil N mineralization rates, and soil C/N and N content were determined for both the forest floor and the 0–20?cm mineral soil in eight jack pine (Pinus banksiana Lamb.) stands in the oil sands region in northern Alberta. Tree growth rates were determined based on changes in tree ring width in the last 6?years and as mean annual aboveground biomass increment.

Results

Soil N availability indices across those forest stands varied and for each stand it was several times higher in the forest floor than in the mineral soil. The in situ and laboratory aerobic and anaerobic soil N mineralization rates, soil mineralized N, in situ N availability measured using PRS probes, soil C/N ratio and N content in both the forest floor and mineral soil, as well as stand age were linearly correlated with tree ring width of jack pine trees across the selected forest stands, consistent with patterns seen in other published studies and suggesting that N availability could be a limiting factor in the range of jack pine stands studied.

Conclusions

In situ and laboratory aerobic and anaerobic N mineralization rates and soil C/N ratio and N content can be used for predicting tree growth in jack pine forests in the oil sand region. Laboratory based measurements such as aerobic and anaerobic N mineralization rates and soil C/N ratio and N content would be preferable as they are more cost effective and equally effective for predicting jack pine growth.     

Declining hydraulic performances and low carbon investments in tree rings predate Scots pine drought-induced mortality

Key message

The retrospective analysis of wood anatomical features evidences how a long-term deterioration of hydraulic performance and carbon use portend drought-induced mortality in Scots pine.

Abstract

Widespread episodes of drought-induced tree mortality are predicted to become more frequent as climate becomes warmer and drier. Nevertheless, growth trends and their links to changes in wood anatomy before tree dies are still poorly understood. Wood anatomical features provide valuable information that can be extracted to infer the mechanisms leading to tree death. In this study, we characterize drought-induced mortality affecting two Scots pine (Pinus sylvestris) sites (Prades and Arcalís) located in the North Eastern Iberian Peninsula. Co-occurring now-dead and living Scots pine trees were sampled and their wood anatomical features were measured and compared. We aimed to detect differences in anatomical features between living and dead trees, and to infer past physiological performances that might have determined their subsequent death or survival. Now-dead trees showed lower tracheid and resin duct production, and smaller radial lumen diameters than co-occurring living trees. At the more xeric Prades site, these anatomical differences were larger and chronic, i.e. were observed over the three studied decades, whilst they were less pronounced at the other, more mesic Arcalís site, where tree mortality episodes were more recent. This indicates that dead trees’ hydraulic conductivity was severely affected and that carbon investment in xylem formation and resin duct production was constrained prior to tree death. Our findings show that both hydraulic deterioration and low carbon allocation to xylem formation were associated to drought-induced mortality in Scots pine. Nevertheless, the temporal dynamics of these processes differed between populations as a function of site climatic conditions.     

Root growth of different oak provenances in two soils under drought stress and air warming conditions

Background and aims

Oaks are considered to be drought- and thermo-tolerant tree species. Nevertheless, species and provenances may differ in their ecological requirements. We hypothesised that (i) provenances from xeric sites are better adapted to drought than those from more humid sites, (ii) oaks direct root growth towards resource-rich layers, and (iii) air-warming promotes root growth.

Methods

To test different provenances of Quercus robur, Q. petraea and Q. pubescens, we conducted a model ecosystem experiment with young trees, grown on acidic and calcareous soil, subjected to drought, air warming, the combination of warming and drought, and a control.

Results

The results were only in partial agreement with the first hypothesis. As expected the provenances originating from drier sites produced more biomass than those from more humid sites under drought conditions. Surprisingly, however, they reacted more sensitive to water limiting conditions, as they produced also substantially more biomass under well-watered conditions. The drought treatment reduced root mass substantially in the upper soil. In agreement with the second hypothesis this led to a shift in the centre of root mass to lower depth, where water was still more available than closer to the soil surface. In contrast to the third hypothesis, the air-warming treatment, which was very mild however compared to climate change scenarios, had no significant effects on root growth.

Conclusions

Given that the provenances from drier sites showed more biomass loss at water limiting conditions than provenances from more humid sites, it remains questionable whether provenances from drier sites are better suited for a future climate.     

Effects of the time of drought occurrence within the growing season on growth and survival of Pinus ponderosa seedlings

Key message

A drought event during spring produces a stronger and long lasting decrease in growth of ponderosa pine seedlings than a summer drought event. However, survival is not differentially affected.

Abstract

Although there is certainty about the increasing frequency of extreme climatic events, the consequences of changing patterns of drought events within the growing season on the growth and survival of different species are much less certain. In particular, little knowledge is available on the differential effect on tree seedlings of a drought event at different times within the growing season. The objective of this study was to quantify the effect of a drought event imposed at different times over the growing season on the growth, survival and some related morphological and physiological variables of Pinus ponderosa seedlings from two seed sources. Four treatments were applied: control conditions; spring drought; summer drought and spring plus summer drought (SpSuD). A drought event in spring reduced stem growth and biomass accumulation in ponderosa pine seedlings during the occurrence of the drought and afterwards, even when plant water status had recovered. The lack of growth recovery could not be associated with loss of stem hydraulic conductivity or reduction in stomatal conductance after drought. However, the spring drought did not differentially affect plant survival, as was the case with prolonged drought in the SpSuD treatment. The summer drought event had a significant but much smaller impact on plant growth. Our results suggest different consequences of a drought event in spring or in summer in ponderosa pine seedlings. This knowledge may be relevant to understand and predict tree seedlings responses to changing patterns of drought events within the growing season in the framework of climatic change.     

Importance of tree height and social position for drought-related stress on tree growth and mortality

Key message

A higher mortality of dominant trees under drought stress is explained by impacts of tree size, canopy- and root structure and the hydraulic transport system.

Abstract

Drought stress can trigger tree mortality but the impact depends on stress intensity (water demand and availability) and on the vulnerability of the individual. Therefore, most research focusses on the species-specific properties such as water use efficiency or hydraulic conductivity that determine vulnerability. At the ecosystem scale, however, tree properties that have been found important for drought sensitivity or resistance vary with individual size and resource availability within a forest—also within the same species. This is caused by different environmental conditions for each tree and hence different growth histories of individuals generating specific anatomical and physiological features. Individual drought stress sensitivity might thus be considerably different from stand scale sensitivity. Indeed, empirical evidence shows that drought stress impact depends on tree social position which can be defined in degrees of suppression but correlated to resource availability, stress sensitivity and stress exposure. In this review, we collect such evidence and discuss the role of microclimate and soil water distribution as well as anatomical and physiological adjustments, which might serve as foundation for better-adapted management strategies to mitigate drought stress impacts. Finally, we define model requirements aiming to capture stand-scale drought responses or management impacts related to drought stress mitigation.

     

Stomatal conductance and intrinsic water use efficiency in the drought year 2003: a case study of European beech

Key message

Beech trees were able to cope with the drought of 2003. Harmful water shortage has been avoided by an effective stomatal closure while use of carbon storage pools may have prevented carbon starvation and growth reduction.

Abstract

We applied hydrodynamic modeling together with a tree ring stable isotope approach to identify the physiological responses of beech trees to changing environmental conditions. The drought conditions of the extreme hot and dry summer in 2003 were hypothesized to significantly influence the radial growth of European beech mainly triggered by the stomatal response towards water scarcity leading, in turn, to a decline in carbon assimilation. The functional–structural single tree modeling approach applied, revealed in fact a strong limitation of water use and carbon gain during drought. However, tree ring width data did not show a clear drought response and no differentiation in radial growth during six subsequent years examined (2002–2007) has been observed. Using integrated results from mechanistic carbon–water balance simulations, tree ring carbon and oxygen isotope analysis and tree ring width measurements we postulate that the suggested drought-induced growth decline has been prevented by the remobilization of stored carbohydrates, an early onset in growth and the relatively late occurrence of the severe drought in 2003. Furthermore, we demonstrate that the stomatal response played a significant role in avoiding harmful water tension that would have caused xylem dysfunction. As a result of the combined investigation with physiological measurements (stable isotope approach) and hydrodynamic modeling of stomatal aperture, we could give insights into the physiological control of mature beech tree functioning under drought. We conclude that beech trees have been operating at their hydraulic limits and that the longer or repeated drought periods would have affected the growth considerably.

     

Longleaf and loblolly pine seedlings respond differently to soil compaction,water content,and fertilization

Aims

Longleaf pine (Pinus palustris Mill.) is being restored across the U.S. South for a multitude of ecological and economic reasons, but our understanding of longleaf pine’s response to soil physical conditions is poor. On the contrary, our understanding of loblolly pine (Pinus taeda L.) root and shoot growth response to soil conditions is well established.

Methods

We performed a comparative greenhouse study which modeled root length density, total seedling biomass, and the ratio of aboveground:belowground mass as functions of volumetric water content, bulk density and soil fertility (fertilized or not).

Results

Root length density was about 35 % greater in longleaf pine seedlings compared to loblolly pine seedlings, and was reasonably well modeled (R ²?=?0.54) for longleaf pine by bulk density (linear), volumetric water content (quadratic), soil fertility, and the interactions of bulk density, volumetric water content, species, and soil fertility. The aboveground:belowground mass ratio (ABR) increased at both extremes of water content.

Conclusions

This research indicates that young longleaf pine seedling root systems respond more negatively to extremes of soil physical conditions than loblolly pine, and compacted or dry loamy soils should be ameliorated in addition to normal competition control, especially on soils degraded by past management.     

Dendrochronological analysis of urban trees: climatic response and impact of drought on frequently used tree species

Key message

Distinct species-specific differences were found in the response to temperature, precipitation and the self-calibrated Palmer Drought Severity Index that are confirmed by pointer year analyzes and superposed epoch analyzes.

Abstract

Trees in urban environments are exposed to heat stress, low air humidity and soil drought. The increasing temperatures and the more frequent heat and drought events will intensify the stress level of urban trees. We applied a dendrochronological approach to evaluate the species-specific suitability under increasing risk of drought of five tree species at highly sealed urban sites in the city of Dresden (Germany). Climate-growth correlation analyses show that temperatures and water availability from April to July in the current year and in summer and autumn of the previous year are the main determining factors for radial growth. However, distinct species-specific differences were found in the response to temperature, precipitation and the self-calibrated Palmer Drought Severity Index. During the study period, the influence of temperature and drought on radial growth during summer months increases for Acer platanoides and Acer pseudoplatanus, whereas no changes occurred for Quercus petraea, Quercus rubra, and P. × hispanica. Pointer year analysis and superposed epoch analyses revealed a species-specific response to extreme climatic events. While for A. platanoides and A. pseudoplatanus a higher number of negative pointer years and significant growth declines in drought years were found, Q. petraea and Q. rubra showed more frequent positive pointer years but no significant growth reductions during drought. Based on these response patterns we classified the studied tree species according to their suitability and drought tolerance for urban sites.     

Soil nutrients and microbial biomass in three contrasting Mediterranean forests

Aims

The extent to which the spatial and temporal patterns of soil microbial and available nutrient pools hold across different Mediterranean forest types is unclear impeding the generalization needed to consolidate our understanding on Mediterranean ecosystems functioning.

Methods

We explored the response of soil microbial, total, organic and inorganic extractable nutrient pools (C, N and P) to common sources of variability, namely habitat (tree cover), soil depth and season (summer drought), in three contrasting Mediterranean forest types: a Quercus ilex open woodland, a mixed Q. suber and Q. canariensis woodland and a Pinus sylvestris forest.

Results

Soil microbial and available nutrient pools were larger beneath tree cover than in open areas in both oak woodlands whereas the opposite trend was found in the pine forest. The greatest differences in soil properties between habitat types were found in the open woodland. Season (drought effect) was the main driver of variability in the pine forest and was related to a loss of microbial nutrients (up to 75 % loss of N_mic and P_mic) and an increase in microbial ratios (C_mic/N_mic, C_mic/P_mic) from Spring to Summer in all sites. Nutrient pools consistently decreased with soil depth, with microbial C, N and P in the top soil being up to 208 %, 215 % and 274 % larger than in the deeper soil respectively.

Conclusions

Similar patterns of variation emerged in relation to season and soil depth across the three forest types whereas the direction and magnitude of the habitat (tree cover) effect was site-dependent, possibly related to the differences in tree species composition and forest structure, and thus in the quality and distribution of the litter input.     

Aleppo pine vulnerability to climate stress is independent of site productivity of forest stands in southeastern Spain

Key message

Clim ate is the main driver of Aleppo pine radial growth variability irrespective of site pro ductivity, with the climate effects on tree growth more limiting from 1970 onwards.

Abstract

Forest management adaptation to climate change requires identifying the previously most vulnerable stands and the possible climate impacts on forests. This study evaluates whether site index, as an indicator of forest productivity, is related to climate–growth responses and assesses the way in which local site factors modulate climate–tree growth relationships. Tree-ring width series and soil characteristics were obtained from six Pinus halepensis stands with different site indices and similar climate. Dendrochronological methods were used to compare tree climate–growth responses among sites and to study temporal trends in inter-annual growth variability and climate–growth relationships (before and after 1970). The influence of topographic and soil features on tree growth was assessed by means of partial least squares. Stands with low site indices tended to present higher mean sensitivities and greater percentages of missing rings, this relation being modulated mainly by clay percentage and nutrient status in soil. Climate is the major Aleppo pine radial growth driver in the study area with similar growth–climate relationship among sites. Radial growth was mainly influenced by spring temperature and precipitation and previous autumn–winter precipitation. This relationship was stronger after 1970 than before this year, showing also a 2-month advancement of the most influential climate variables after 1970, from May to March. These results and the increasing temporal trend found in mean sensitivity after 1970 highlight the vulnerability of these stands to climate change. Site index was not found to be directly related to stand vulnerability, although local site factors modulate in part the tree-growth response.     

Tree-ring wood anatomy and stable isotopes show structural and functional adjustments in olive trees under different water availability

Background and Aims

Olive tree (Olea europaea L.) is a drought-tolerant tree species cultivated in Mediterranean-type environments. Although it is tolerant to drought, dry conditions decrease its productivity. A thorough analysis of the hydraulic architecture and wood anatomical plasticity, as well as of their physiological significance, is needed to understand how olive trees will adapt to the predicted increase in frequency and severity of drought in the Mediterranean region.

Methods

Dendrochronological, stable isotopic (δ¹³C, δ¹⁸O) and wood anatomical analyses were applied to understand how different water availability can affect wood stem structure and function, in rainfed and irrigated at 100 % of crop evapotranspiration (ETc) olive trees in an experimental orchard close to Benevento (Italy) from 1992 to 2009.

Results

Dendrochronological data indicate that cross-dating and synchronization of ring-width time series in olive tree is possible. After the start of irrigation, significantly more negative δ¹³C and lower δ¹⁸O values were recorded in irrigated trees indicating higher stomatal conductance and transpiration rates. Increased water balance induced the formation of a higher number of vessels with higher diameter.

Conclusions

Water balance variations affected wood anatomy and isotopic composition. Anatomical analyses detected structural and functional adjustments in rainfed trees that produced more vessels with lower diameter to prevent cavitation. Isotopic analyses confirmed that irrigated trees continuously showed enhanced transpiration rates.     

Hydraulic limitation on maximum height of Pinus strobus trees in northern Minnesota,USA

Key message

Using comparisons within and between trees, the authors show evidence for hydraulic limitation of tree height in a humid-climate species that is far from the global maximum tree height.

Abstract

We measured water status and two indicators of drought stress as a function of height within the canopies of four tall (32–35 m) eastern white pines (Pinus strobus) at an old-growth site in northern Minnesota, USA. Pre-dawn and midday xylem pressure potential measured on terminal shoots (Ψ _shoot), needle length, and foliar carbon isotope discrimination (δ ¹³C) all showed within-canopy gradients consistent with increasing drought stress with height. Midday Ψ _shoot near tree tops was ?1.8 MPa, close to values associated with stomatal closure for other temperate conifers. Pre-dawn Ψ _shoot decreased with height at >2× the gradient in gravitational potential. δ ¹³C was strongly correlated with height and weakly correlated with light. Needles were 15–25 % shorter at canopy top compared to the bottom of the canopy. Midday Ψ _shoot and needle length showed significant differences in regression model coefficients from tree to tree. The patterns are consistent with hydraulic constraints on height growth of white pine at this site.     

Shoot growth, root growth and resource capture under limiting water and N supply for two cultivars of lettuce (Lactuca sativa L.)

Background and aims

To improve vegetable crops adapted to low input and variable resource availability, better understanding is needed of root system functioning, including nitrogen and water capture.

Methods

This study quantified shoot and root development and patterns of water and nitrate capture of two lettuce cultivars subjected to temporary drought at two development stages (Trial 1) or to continuous, localized drought and/or nitrate shortage (Trial 2).

Results

In Trial 1, early drought slowed down shoot and root growth, whereas late drought enhanced root proliferation in the top 0.1 m. Nitrate capture during drought was sustained by increased nitrate inflow from deeper layers. Plants did not recover fully from drought after re-watering. In Trial 2, root proliferation was stimulated in the drier soil compartment partially compensating reduced water availability and nitrate mobility. Under nitrate shortage, root proliferation was enhanced in the compartment where nitrate was more abundant, irrespective of water availability.

Conclusions

Changes observed in the root system are ‘feed-forward’ mechanisms to sustain resource capture in a limiting growing environment. The type of stress (drought or nitrate shortage) affects coping strategies; nitrate concentration in the soil solution, combined with the nutritional status of the plant will determine the stress response.     

Effect of ecological factors on intra-annual stem girth increment of holm oak

Key message

The intra-annual stem girth increment of Quercus ilex is mainly driven by water availability and secondly by temperature. Tree size and competition modulate the growth response to climate.

Abstract

Holm oak (Quercus ilex ssp. ballota [Desf.] Samp.) is the most widespread species in the Iberian peninsula, being one of the most representative trees in forests and open woodlands. The analysis of stem girth increment of holm oak may provide valuable information about how Mediterranean ecosystems will respond to the forecasted climate changes. However, due to the variability of the Mediterranean climate, the knowledge of intra-annual patterns of growth is needed for a better understanding of the influence of the climatic variables at this scale. To this end, we used band dendrometers to measure monthly stem girth increments of 96 holm oak trees from 2003 to 2010, located in open woodlands and dense Mediterranean forests in southwestern Spain. We assessed the effects of climate, competition, topography, and initial stem diameter on stem girth increment. The major stem increment periods were in spring and autumn whereas increment rates were very low or even negative in winter and summer. Spring was not every year the season with the higher stem increments, but autumn when spring was very dry. Higher precipitation, soil moisture, and relative humidity had significant positive effects on stem increment, whereas higher temperature, reference evapotranspiration, and solar radiation had significant negative effects. Initial tree diameter and competition from nearby trees partly explained significant differences in stem increment of individual trees. Therefore, the forecasted climatic changes, in which decreased rainfall in spring and increased summer drought are expected in the Mediterranean region, may be a significant threat to the Q. ilex ecosystems.     

Variation in woody plant mortality and dieback from severe drought among soils, plant groups, and species within a northern Arizona ecotone

Vegetation change from drought-induced mortality can alter ecosystem community structure, biodiversity, and services. Although drought-induced mortality of woody plants has increased globally with recent warming, influences of soil type, tree and shrub groups, and species are poorly understood. Following the severe 2002 drought in northern Arizona, we surveyed woody plant mortality and canopy dieback of live trees and shrubs at the forest–woodland ecotone on soils derived from three soil parent materials (cinder, flow basalt, sedimentary) that differed in texture and rockiness. Our first of three major findings was that soil parent material had little effect on mortality of both trees and shrubs, yet canopy dieback of trees was influenced by parent material; dieback was highest on the cinder for pinyon pine (Pinus edulis) and one-seed juniper (Juniperus monosperma). Ponderosa pine (Pinus ponderosa) dieback was not sensitive to parent material. Second, shrubs had similar mortality, but greater canopy dieback, than trees. Third, pinyon and ponderosa pines had greater mortality than juniper, yet juniper had greater dieback, reflecting different hydraulic characteristics among these tree species. Our results show that impacts of severe drought on woody plants differed among tree species and tree and shrub groups, and such impacts were widespread over different soils in the southwestern U.S. Increasing frequency of severe drought with climate warming will likely cause similar mortality to trees and shrubs over major soil types at the forest–woodland ecotone in this region, but due to greater mortality of other tree species, tree cover will shift from a mixture of species to dominance by junipers and shrubs. Surviving junipers and shrubs will also likely have diminished leaf area due to canopy dieback.     

Increasing phosphorus limitation along three successional forests in southern China

Background and Aims

Phosphorus (P) is commonly one of most limiting nutrients in tropical and subtropical forests, but whether P limitation would be exacerbated during forest succession remains unclear.

Methods

Soil phosphatase activity is often used as an indicator of P limitation. Here we examined soil acid phosphatase activity (APA) underneath tree species in pine forest (PF), mixed pine and broadleaf forest (MF) and monsoon evergreen broadleaf forest (MEBF) which represented the early, middle and late successional stages of subtropical forests in China, respectively. We also analyzed other indicators of P status (soil available P and N and P stoichiometry of the tree species).

Results

APA or APA per unit soil organic carbon under tree species was relatively low in the early successional forest. Different from PF and MF, soil available P beneath the tree species was lower than in the bulk soils in MEBF. Soil APA was closely related to N:P ratios of tree species across all three forests.

Conclusions

Our results imply that P limitation increases during forest succession at our site. The dominant tree species with low soil APAs in MEBF are likely more P-limited than other tree species.     

Root plasticity maintains growth of temperate grassland species under pulsed water supply

Background and aims

The frequency of rain is predicted to change in high latitude areas with more precipitation in heavy, intense events interspersed by longer dry periods. These changes will modify soil drying cycles with unknown consequences for plant performance of temperate species.

Methods

We studied plant growth and root traits of juveniles of four grasses and four dicots growing in a greenhouse, when supplying the same total amount of water given either regular every other day or pulsed once a week.

Results

Pulsed water supply replenished soil moisture immediately after watering, but caused substantial drought stress at the end of the watering cycle, whereas regular watering caused more moderate but consistent drought. Grasses had lower water use efficiency in the pulsed watering compared to regular watering, whereas dicots showed no difference. Both grasses and dicots developed thinner roots, thus higher specific root length, and greater root length in the pulsed watering. Growth of dicots was slightly increased under pulsed watering.

Conclusions

Temperate species coped with pulsed water supply by eliciting two responses: i) persistent shoot growth, most likely by maximizing growth at peaks of soil moisture, thus compensating for slower growth during drought periods; ii) plasticity of root traits related to increased resource uptake. Both responses likely account for subtle improvement of growth under changed water supply conditions.