Predation on northern shrimp (Pandalus borealis) by three gadoid species

Northern shrimp (Pandalus borealis) is targeted by commercial fisheries, but is also an important prey in the marine food web. In this study, stomach content data were used to study predation on shrimp by three gadoid species, cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus), in six inshore areas around Iceland. The results showed that shrimp was more important in the diet of cod compared with the other two predators. However, the overall predation pressure was similar for cod and haddock due to the high abundance of haddock. Therefore, even though shrimp is not the primary source of food for haddock, this species can have a substantial effect on shrimp stocks when haddock abundance is high. In addition, while cod and haddock did not select for any particular size of shrimp, whiting seemed to preferentially target juvenile shrimp. The results suggest that due to the overall effects of these three predators on shrimp stocks, gadoids need to be included in the management of shrimp stocks as predation is one of the major drivers in the development of this important prey stock.     

Disentangling factors limiting diamondback moth,Plutella xylostella (L.), spatio‐temporal population abundance: A tool for pest forecasting

Data‐mining techniques play an important role in hyperparameter optimization of heterogeneous environmental factors and their relative contribution as determinants of incidences in insect pest ecological studies. A multidimensional field‐based surveillance was conducted in two seasons (24 months), July–June of each season (2015/2016 ‐ season 1 and 2016/2017 ‐ season 2) using sex‐pheromone‐baited traps and Thermocron i‐Buttons to identify key determinants of population abundance of diamondback moth, Plutella xylostella L., across spatial horticultural hotspots of Botswana. The moth is a notorious global brassica pest. Pearson's product moment correlation matrix showed month of the year (M), mean temperature (T_mean) and maximum temperature (T_max) as positively correlated (p < 0.001) to number of moths (N), while minimum temperature (T_min), minimum relative humidity (RH_min), mean relative humidity (RH_mean), maximum relative humidity (RH_max) and host plant (h) were negatively correlated (p < 0.001) to N. Using Waikato Environment for Knowledge Analysis (WEKA) data‐mining techniques, two models were developed: (a) M5P decision‐tree algorithm associated with nine linear models (LMs) and (b) principal component analysis (PCA) based on four principal components. Both approaches identified M as the major predictor of moth abundance, followed by h and farming region (R). However, R was a function of T_max (positive auto‐correlation) and RH_max (negative auto‐correlation). These results provide simplified relative contribution of heterogeneous factors in influencing P. xylostella spatio‐temporal abundance, essential for early warning systems in pest management. This is an important component of sustainable pest management aimed at managing insect pests and minimizing pesticides abuse in brassica production systems.     

The mobile epifauna of the soft bottoms in the subtidal Oosterschelde estuary: structure,function and impact of the storm-surge barrier

Data on the mobile epifauna of the Oosterschelde estuary, collected by beam trawl, were compiled from several studies. Multivariate statistical techniques brought out the fact that the Oosterschelde, when compared with neighbouring areas, has a characteristic epibenthic fauna. Diversity as measured by Hill's diversity numbers N through N ₊ , is higher for the Oosterschelde (N₁ = 4.5) than for the Voordelta (N₁ = 3.5) and the Westerschelde (N₁ = 2.2).Four epifaunal communities can be distinguished within the Oosterschelde, the two most seaward communities being the richest. Annual production is estimated at about 6 gADW m^–2 yr^–1, annual consumption is estimated at over 25 gADW m^–2 yr^–1. These results are highly dependent on the assumptions. Over 85% of the epibenthic production and consumption in the Oosterschelde is accounted for by only six species: starfish Asterias rubens, plaice Pleuronectes platessa, bib Trisopterus luscus, brown shrimp Crangon crangon, shore crab Carcinus maenas and dab Limanda limanda. In spite of its abundance, the sand goby Pomatoschistus minutus contributes little to the production.From the available data it is difficult to assess the impact of the construction of the storm-surge barrier and the compartmentalization dams on the epibenthic fauna. The increase in flatfish in the Hammen area is probably linked to the decrease in current velocities in that area. On the other hand the increase in the gadoids bib and whiting Merlangius merlangus is predominantly due to the stronger year classes in the post-barrier time period. Lower nutrient inputs through the Northern branch, in combination with the increase of the gadoids, may have caused the decline of the brown shrimp in the Oosterschelde. A decrease has also been observed in the sandeel Ammodytes tobianus and the hooknose Agonus cataphractus.     

Strong thermal acclimation of photosynthesis in tropical and temperate wet‐forest tree species: the importance of altered Rubisco content

Understanding of the extent of acclimation of light‐saturated net photosynthesis (A_n) to temperature (T), and associated underlying mechanisms, remains limited. This is a key knowledge gap given the importance of thermal acclimation for plant functioning, both under current and future higher temperatures, limiting the accuracy and realism of Earth system model (ESM) predictions. Given this, we analysed and modelled T‐dependent changes in photosynthetic capacity in 10 wet‐forest tree species: six from temperate forests and four from tropical forests. Temperate and tropical species were each acclimated to three daytime growth temperatures (T_growth): temperate – 15, 20 and 25 °C; tropical – 25, 30 and 35 °C. CO₂ response curves of A_n were used to model maximal rates of RuBP (ribulose‐1,5‐bisphosphate) carboxylation (V_cmax) and electron transport (J_max) at each treatment's respective T_growth and at a common measurement T (25 °C). SDS‐PAGE gels were used to determine abundance of the CO₂‐fixing enzyme, Rubisco. Leaf chlorophyll, nitrogen (N) and mass per unit leaf area (LMA) were also determined. For all species and T_growth, A_n at current atmospheric CO₂ partial pressure was Rubisco‐limited. Across all species, LMA decreased with increasing T_growth. Similarly, area‐based rates of V_cmax at a measurement T of 25 °C (V_cmax²⁵) linearly declined with increasing T_growth, linked to a concomitant decline in total leaf protein per unit leaf area and Rubisco as a percentage of leaf N. The decline in Rubisco constrained V_cmax and A_n for leaves developed at higher T_growth and resulted in poor predictions of photosynthesis by currently widely used models that do not account for T_growth‐mediated changes in Rubisco abundance that underpin the thermal acclimation response of photosynthesis in wet‐forest tree species. A new model is proposed that accounts for the effect of T_growth‐mediated declines in V_cmax²⁵ on A_n, complementing current photosynthetic thermal acclimation models that do not account for T sensitivity of V_cmax²⁵.     

Gas exchanges of an endangered species Syringa pinnatifolia and a widespread congener S. oblata

Net photosynthetic rate (P _N), transpiration rate (E), water use efficiency (WUE), stomatal conductance (g _s), and stomatal limitation (L_s) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m^-2s^-1 for S. pinnatifolia and 1 700 µmol m^-2s^-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g_s. Unlike S. oblata, the maximal photosynthetic rate (P _max) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower P _N together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia.This revised version was published online in March 2005 with corrections to the page numbers.     

Sage-Grouse Population Dynamics are Adversely Affected by Overabundant Feral Horses

In recent decades, feral horse (Equus caballus; horse) populations increased in sagebrush (Artimesia spp.) ecosystems, especially within the Great Basin, to the point of exceeding maximum appropriate management levels (AML_max), which were set by land administrators to balance resource use by feral horses, livestock, and wildlife. Concomitantly, greater sage-grouse (Centrocercus urophasianus; sage-grouse) are sagebrush obligates that have experienced population declines within these same arid environments as a result of steady and continued loss of seasonal habitats. Although a strong body of research indicates that overabundant populations of horses degrade sagebrush ecosystems, empirical evidence linking horse abundance to sage-grouse population dynamics is missing. Within a Bayesian framework, we employed state-space models to estimate population rate of change (λ) using 15 years (2005–2019) of count surveys of male sage-grouse at traditional breeding grounds (i.e., leks) as a function of horse abundance relative to AML_max and other environmental covariates (e.g., wildfire, precipitation, % sagebrush cover). Additionally, we employed a post hoc impact-control design to validate existing AML_max values as related to sage-grouse population responses, and to help control for environmental stochasticity and broad-scale oscillations in sage-grouse abundance. On average, for every 50% increase in horse abundance over AML_max, our model predicted an annual decline in sage-grouse abundance by 2.6%. Horse abundance at or below AML_max coincided with sage-grouse λ estimates that were consistent with trends at non-horse areas elsewhere in the study region. Thus, AML_max, as a whole, appeared to be set adequately in preventing adverse effects to sage-grouse populations. Results indicated 76%, 97%, and >99% probability of sage-grouse population decline relative to controls when horse numbers are 2, 2.5, and ≥3 times over AML_max, respectively. As of 2019, horse herds exceeded AML_max in Nevada, USA, by >4 times on average across all horse management areas. If feral horse populations continue to grow at current rates unabated, model projections indicate sage-grouse populations will be reduced within horse-occupied areas by >70.0% by 2034 (15-year projection), on average compared to 21.2% estimated for control sites. A monitoring framework that improves on estimating horse abundance and identifying responses of sage-grouse and other key indicator species (plant and animal) would be beneficial to guide management decisions that promote co-occurrence of horses with sensitive wildlife and livestock within landscapes subjected to multiple uses. Published 2021. This article is a U.S. Government work and is in the public domain in the USA. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Thermal response of demersal and pelagic juvenile fishes from the surf zone during a heat‐wave simulation

Experimental measurements were collected in the laboratory to evaluate the maximum thermal limit and thermal plasticity of Neotropical juvenile fish with different life habitats (demersal and pelagic) from surf zone in response to a “heat‐wave experiment”. Trials were conducted using two temperature acclimations (T_a), including the current average temperature of Southeastern Brazil (T_a: 14 days at 25°C) and the “heat‐wave experiment” (T_a: 14 days at 30°C), simulating a heat‐wave event that occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5°C. Typical species of the surf zone were used: the demersal White sea catfish (Genidens barbus) and Gulf kingcroaker (Menticirrhus littoralis), and the pelagic fishes Great pompano (Trachinotus goodei) and Long‐fin mullet (Mugil brevirostris). The thermal range and plasticity values for the both life‐habitats species were verified through current and heat‐wave acclimation. The thermal tolerance at high temperatures (CT_max) of these species differed between T_a, habitat and species. Fish showed a species‐specific response to temperature increase, regardless of their habitat even under similar abiotic conditions. However, at the heat‐wave simulation, the demersal fish presented a greater thermal plasticity in relation to the pelagic fish. Despite the higher thermal tolerance when exposed to heat‐wave simulation, all fish species displayed a lower thermal edge safety that is markedly close to their maximum thermal limits.     

Cost-benefit relationships in sclerophyllous leaves of the ‘Bana’ vegetation in the Amazon region

This study estimated the construction const (CC) and maintenance cost (MC) of leaf tissue on the basis of dry mass (CC_Mass, MC_Mass) and leaf area (CC_Area, MC_Area), as well as the maximum leaf gas exchange capacity, so as to examine leaf cost:benefit relationship in six dominant species of the ‘Bana’ vegetation. Minimum and maximum CC_Mass averaged 1.71 ± 0.03 and 1.78 ± 0.03 g glucose g⁻¹. The CC_Mass showed a statistically significant positive correlation with crude fibre, and tended to decline as leaves were larger. Thus, smaller leaves tended to be built out of a more expensive material than that found in species bearing larger leaves. The average CC_Area of the ‘Bana’ species was 376 ± 15 g glucose m⁻². A robust correlation was found between CC_Area with leaf dry mass to leaf area ratio, as well as with leaf thickness, but not with leaf density. MC_Mass (g glucose g⁻¹ day⁻¹) and MC_Area (g glucose m⁻² day⁻¹⁾ were positively correlated. Maximum and minimum MC_Mass increased significantly with protein and lipid content, respectively. Maximum carbon assimilation (A _max) was positively correlated with CC_Area. All the species operated at high stomatal conductance (g _s) and C _i/C _a which suggested low short-term water use efficiency. Potential nitrogen use efficiency (PNUE = A _max/N) averaged 35.4 ± 1.8 mmol CO₂ mol⁻¹ N. As the sclerophylly index (g crude fibre g⁻¹ protein) increased, the ratio of CC_Area to A _max increased significantly. This result suggests a trade-off between investments in an expensive resistant sclerophyllous leaf which should maximize carbon gain in the long term.     

Irradiance acclimation,capture ability,and efficiency in invasive and non-invasive alien plant species

We tested the hypothesis that invasive (IN) species could capture resources more rapidly and efficiently than noninvasive (NIN) species. Two IN alien species, Ageratina adenophora and Chromolaena odorata, and one NIN alien species, Gynura sp. were compared at five irradiances. Photon-saturated photosynthetic rate (P _max), leaf mass (LMA) and nitrogen content (N_A) per unit area, and photosynthetic nitrogen utilization efficiency (PNUE) increased significantly with irradiance. LMA, N_A, and PNUE all contributed to the increased P _max, indicating that both morphological and physiological acclimation were important for the three alien species. Under stronger irradiance, PNUE was improved through changes in N allocation. With the increase of irradiance, the amount of N converted into carboxylation and bioenergetics increased, whereas that allocated to light-harvesting components decreased. The three alien species could adequately acclimate to high irradiance by increasing the ability to utilize and dissipate photon energy and decreasing the efficiency of photon capture. The two IN species survived at 4.5 % irradiance while the NIN species Gynura died, representing their different invasiveness. Ageratina generally exhibited higher respiration rate (R _D) and N_A. However, distinctly higher P _max, PNUE, P _max/R _D, or P _max/LMA were not detected in the two invasive species, nor was lower LMA. Hence the abilities to capture and utilize resources were not always associated with invasiveness of the alien species.     

Effects of root architecture, physical tree characteristics, and soil shear strength on maximum resistive bending moment for overturning Salix babylonica and Juglans ailanthifolia

Effects of root architecture, physical tree characteristics, and soil shear strength on overturning moment due to flooding were investigated using Salix babylonica and Juglans ailanthifolia, exotic and invasive plants in Japanese rivers. Tree-pulling experiments that simulated flood action were conducted, and the resulting damage was examined to assess the effects of physical tree characteristics and root architecture on the maximum resistive bending moment (M _max) for overturning. In situ soil shear strength tests were conducted to measure soil strength parameters. The effects of species differences on the M _max were examined by analyzing root architecture. S. babylonica has a heart-root system that produces a greater overturning moment due to the strong root anchorage and the large amount of substrate that must be mobilized during overturning. J. ailanthifolia has a plate-root system that produces a smaller overturning moment. However, trees with the plate-root system may withstand overturning better due to an increased root:shoot ratio. The results of the study show that the M _max of a tree for overturning had significant (P < 0.05) correlations with a tree’s physical characteristics, including height (H), trunk diameter at breast height (D _bh), D _bh², height multiplied by the second power of D _bh (trunk volume index H × D _bh²), and root–soil plate depth (R _d), and root–soil plate radius (R _r). Considering the strategy of J. ailanthifolia to increase the root:shoot ratio for anchoring in the substrate, the trunk volume index (H × D _bh²) is a better parameter than D _bh² because it indirectly involves the difference in below-ground volume and surface area. Different soil cohesion values were found at different experimental sites, and the average M _max for overturning each species decreased linearly with increasing soil cohesion.     

Assessment of ploidy level on stress tolerance of <Emphasis Type="Italic">Cenchrus</Emphasis> species based on leaf photosynthetic characteristics

Many species of the genus Cenchrus, with different ploidy are important components of world grasslands. In the present investigation, influence of ploidy on leaf water potential (Ψ_leaf) and photosynthetic characteristics under water-stress condition was studied in 2-month-old plants of eight Cenchrus species representing three ploidy and two life spans. Stress was imposed for 2, 4, 6, and 8 days by withholding watering. Decrease in water potential, chlorophyll content, photosynthetic rate (P _N), stomatal conductance for CO₂ (g _s), and carboxylation efficiency (P _N/C _i) occurred in all species. Nevertheless, perennial and diploid C. setigerus maintained the highest P _N/C _i at maximum stress indicating its higher assimilation potential. Photosynthetic water use efficiency (P _N/E) in general decreased with increase of water stress; however, at low stress, reverse trend was observed in diploid C. prieurri, C. setigerus, and tetraploid C. glaucus. Results indicate that relative reduction in photosynthetic characteristics was more in annual diploid than perennial diploid and tetraploid. Stress tolerance in terms of plant height, rolling and wilting of leaves also indicated better adaptability of tetra and hexaploid species over diploid. Moreover, recovery of different physiological traits was more pronounced in perennial tetraploid and hexaploid over annual diploid, thus making them suited more to drought conditions. Analysis of variance results showed direct correlation (r = 0.675) of ploidy with gas exchange parameters indicating better impact of this on physiological performance of different species of Cenchrus under water stress. This is the first report where influence of ploidy levels on photosynthetic characteristics and overall responses to moisture stress is studied in a tropical grass species.     

Spatial and temporal variation in nitrogen fixation and its importance to phytoplankton in phosphorus‐rich lakes

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Predicting tropical plant physiology from leaf and canopy spectroscopy

A broad regional understanding of tropical forest leaf photosynthesis has long been a goal for tropical forest ecologists, but it has remained elusive due to difficult canopy access and high species diversity. Here we develop an empirical model to predict sunlit, light-saturated, tropical leaf photosynthesis using leaf and simulated canopy spectra. To develop this model, we used partial least squares (PLS) analysis on three tropical forest datasets (159 species), two in Hawaii and one at the biosphere 2 laboratory (B2L). For each species, we measured light-saturated photosynthesis (A), light and CO₂ saturated photosynthesis (A _max), respiration (R), leaf transmittance and reflectance spectra (400–2,500 nm), leaf nitrogen, chlorophyll a and b, carotenoids, and leaf mass per area (LMA). The model best predicted A [r ²  = 0.74, root mean square error (RMSE) = 2.9 μmol m⁻² s⁻¹)] followed by R (r ²  = 0.48), and A _max (r ²  = 0.47). We combined leaf reflectance and transmittance with a canopy radiative transfer model to simulate top-of-canopy reflectance and found that canopy spectra are a better predictor of A (RMSE = 2.5 ± 0.07 μmol m⁻² s⁻¹) than are leaf spectra. The results indicate the potential for this technique to be used with high-fidelity imaging spectrometers to remotely sense tropical forest canopy photosynthesis.     

A mitogenomic approach to the taxonomy of pollocks: <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> and <Emphasis Type="Italic">T. finnmarchica</Emphasis> represent one single species

Background  

The walleye pollock (Theragra chalcogramma) and Norwegian pollock (T. finnmarchica) are confined to the North Pacific and North Atlantic Oceans, respectively, and considered as distinct species within the family Gadidae. We have determined the complete mtDNA nucleotide sequence of two specimens of Norwegian pollock and compared the sequences to that of 10 specimens of walleye pollock representing stocks from the Sea of Japan and the Bering Sea, 2 specimens of Atlantic cod (Gadus morhua), and 2 specimens of haddock (Melanogrammus aeglefinus).     

Population genetics of the American eel (Anguilla rostrata): FST = 0 and North Atlantic Oscillation effects on demographic fluctuations of a panmictic species

We performed population genetic analyses on the American eel (Anguilla rostrata) with three main objectives. First, we conducted the most comprehensive analysis of neutral genetic population structure to date to revisit the null hypothesis of panmixia in this species. Second, we used this data to provide the first estimates of contemporary effective population size (N_e) and to document temporal variation in effective number of breeders (N_b) in American eel. Third, we tested for statistical associations between temporal variation in the North Atlantic Oscillation (NAO), the effective number of breeders and two indices of recruit abundance. A total of 2142 eels from 32 sampling locations were genotyped with 18 microsatellite loci. All measures of differentiation were essentially zero, and no evidence for significant spatial or temporal genetic differentiation was found. The panmixia hypothesis should thus be accepted for this species. N_b estimates varied by a factor of 23 among 12 cohorts, from 473 to 10 999. The effective population size N_e was estimated at 10 532 (95% CI, 9312–11 752). This study also showed that genetically based demographic indices, namely N_b and allelic richness (Ar), can be used as surrogates for the abundance of breeders and recruits, which were both shown to be positively influenced by variation during high (positive) NAO phases. Thus, long‐term genetic monitoring of American glass eels at several sites along the North American Atlantic coast would represent a powerful and efficient complement to census monitoring to track demographic fluctuations and better understand their causes.     

N<Subscript>2</Subscript> fixation in three perennial <Emphasis Type="Italic">Trifolium</Emphasis> species in experimental grasslands of varied plant species richness and composition

This study is the first to investigate quantitative effects of plant community composition and diversity on N₂ fixation in legumes. N₂ fixation in three perennial Trifolium species grown in field plots with varied number of neighbouring species was evaluated with the ¹⁵N natural abundance method (two field sites, several growing seasons, no N addition) and the isotope dilution method (one site, one growing season, 5 g N m⁻²). The proportion of plant N derived from N₂ fixation, pNdfa, was generally high, but the N addition decreased pNdfa, especially in species-poor communities. Also following N addition, the presence of grasses in species-rich communities increased pNdfa in T. hybridum and T. repens L., while legume abundance had the opposite effect. In T. repens, competition for light from grasses appeared to limit growth and thereby the amount of N₂ fixed at the plant level, expressed as mg N₂ fixed per sown seed. We conclude that the occurrence of diversity effects seems to be largely context dependent, with soil N availability being a major determinant, and that species composition and functional traits are more important than species richness regarding how neighbouring plant species influence N₂ fixation in legumes.     

Physiological responses to nitrogen and sulphur addition and raised temperature in <Emphasis Type="Italic">Sphagnum balticum</Emphasis>

Sphagnum, the main genus which forms boreal peat, is strongly affected by N and S deposition and raised temperature, but the physiological mechanisms behind the responses are largely unknown. We measured maximum photosynthetic rate (NP_max), maximum efficiency of photosystem II [variable fluorescence (F _v)/maximum fluorescence yield (F _m)] and concentrations of N, C, chlorophyll and carotenoids as responses to N and S addition and increased temperature in Sphagnum balticum (a widespread species in the northern peatlands) in a 12-year factorial experiment. NP_max did not differ between control (0.2 g N m⁻² year⁻¹) and high N (3.0 g N m⁻² year⁻¹), but was higher in the mid N treatment (1.5 g N m⁻² year⁻¹). N, C, carotenoids and chlorophyll concentration increased in shoot apices after N addition. F _v/F _m did not differ between N treatments. Increased temperature (+3.6°C) had a small negative effect on N concentration, but had no significant effect on NP_max or F _v/F _m. Addition of 2 g S m⁻² year⁻¹ showed a weak negative effect on NP_max and F _v/F _m. Our results suggest a unimodal response of NP_max to N addition and tissue N concentration in S. balticum, with an optimum N concentration for photosynthetic rate of ~13 mg N g⁻¹. In conclusion, high S deposition may reduce photosynthetic capacity in Sphagnum, but the negative effects may be relaxed under high N availability. We suggest that previously reported negative effects on Sphagnum productivity under high N deposition are not related to negative effects on the photosynthetic apparatus, but differences in optimum N concentration among Sphagnum species may affect their competitive ability under different N deposition regimes.     

A coupled model of stomatal conductance and photosynthesis for winter wheat

The model couples stomatal conductance (g _s) and net photosynthetic rate (P _N) describing not only part of the curve up to and including saturation irradiance (I _max), but also the range above the saturation irradiance. Maximum stomatal conductance (g _smax) and I _max can be calculated by the coupled model. For winter wheat (Triticum aestivum) the fitted results showed that maximum P _N (P _max) at 600 μmol mol⁻¹ was more than at 350 μmol mol⁻¹ under the same leaf temperature, which can not be explained by the stomatal closure at high CO₂ concentration because g _smax at 600 μmol mol⁻¹ was less than at 350 μmol mol⁻¹. The irradiance-response curves for winter wheat had similar tendency, e.g. at 25 °C and 350 μmol mol⁻¹ both P _N and g _s almost synchronously reached the maximum values at about 1 600 μmol m⁻² s⁻¹. At 25 °C and 600 μmol mol⁻¹ the I _max corresponding to P _max and g _smax was 2 080 and 1 575 μmol m⁻² s⁻¹, respectively.     

Susceptibility to photoinhibition in seedlings of six tropical fruit tree species native to Malaysia following transplantation to a degraded land

To investigate the adaptive capacity to a strong light environment when planted on degraded land, we examined photosynthetic properties in relation to photoinhibition for the sun-leaves of six tropical fruit tree species native to Malaysia before and after transplanting. The six species were: Bouea macrophylla (Bm), Callerya atropurpurea (Ca), Canarium pilosum (Cp), Cynometra cauliflora (Cc), Morinda citrifolia (Mc) and Syzygium sp. (Ssp), which produce edible fruit for endemic animals and birds, and are candidates for corridor plantations. Based on the measurements performed before transplanting, the degree of chronic photoinhibition indicated by the decrease in pre-dawn F _v/F _m was well associated with an accumulation of excessive excitation energy in PSII indicated by a decrease in photochemical quenching (qP). Among the species, Ca and Mc showed lower degrees of photoinhibition with higher qP. Higher electron transport rates (ETR) were observed with higher qP whereas there was no significant relationship between regulatory thermal dissipation (indicated by ) and qP. Energy dissipation via electron transport was suggested to be important in keeping qP high and preventing photoinhibition when compared among species. Cc and Bm showed lower ETR and higher susceptibility to photoinhibition before and after transplanting. New Cp and Mc leaves developed after transplanting showed increased area-based leaf nitrogen content (N _area) and stomatal conductance (gs) compared with those before transplanting resulting in higher light-saturated net photosynthetic rates (A _max) and ETR, and contributing to mitigate photoinhibition. In contrast to these species, Ca achieved high A _max with a water conservative manner (indicated by its relatively lower gs), where the higher carboxylation efficiency accompanied with the higher N _area allowed them to maintain relatively high A _max and ETR at lower intercellular CO₂ concentration.     

Effects of elevated [CO2] on photosynthesis in European forest species: a meta-analysis of model parameters

The effects of elevated atmospheric CO₂ concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, process-based computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO₂] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A_max), the potential electron transport rate (J_max), the maximum Rubisco activity (V_cmax) and leaf nitrogen concentration on mass (N_m) and area (N_a) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO₂]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO₂ concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J_max and V_cmax of the order of 10%. This reduction in J_max and V_cmax was linked to the effects of elevated [CO₂] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO₂]. Tables of model parameter values for different European forest species are given.