Nitrogen addition promotes terrestrial plants to allocate more biomass to aboveground organs: A global meta-analysis

A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m⁻² year⁻¹) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%–32.1%) and 14.7% (11.6%–17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition.     

Changes in woody vegetation abundance and diversity after natural disturbances causing different levels of mortality

Questions: How does woody vegetation abundance and diversity differ after natural disturbances causing different levels of mortality? Location: Abies balsamea–Betula papyrifera boreal mixed‐wood stands of southeast Quebec, Canada. Methods: Woody vegetation abundance and diversity were quantified and compared among three disturbance‐caused mortality classes, canopy gap, moderate‐severity disturbances, and catastrophic fire, using redundancy analysis, a constrained linear ordination technique, and diversity indices. Results: Substantial changes in canopy tree species abundance and diversity only occurred after catastrophic fire. Shade‐tolerant, late‐successional conifer species remained dominant after canopy gap and moderate‐severity disturbances, whereas shade‐intolerant, early‐successional colonizers dominated canopy tree regeneration after catastrophic fire. Density and diversity of mid‐tolerant and shade‐intolerant understory tree and shrub species increased as the impact of disturbance increased. Highest species richness estimates were observed after catastrophic fire, with several species establishing exclusively under these conditions. Relative abundance of canopy tree regeneration was most similar after canopy gap and moderate‐severity disturbances. For the sub‐canopy tree and shrub community, relative species abundances were most similar after moderate‐severity disturbances and catastrophic fire. Vegetation responses to moderate‐severity disturbances thus had commonalities with both extremes of the disturbance‐caused mortality gradient, but for different regeneration layers. Conclusions: Current spatio‐temporal parameters of natural disturbances causing varying degrees of mortality promote the development of a complex, multi‐cohort forest condition throughout the landscape. The projected increase in time intervals between catastrophic fires may lead to reduced diversity within the system.     

Proteomic identification of predictive biomarkers of resistance to neoadjuvant chemotherapy in luminal breast cancer: a possible role for 14-3-3 theta/tau and tBID?

Introduction

Chemotherapy resistance is a major obstacle in effective neoadjuvant treatment for estrogen receptor-positive breast cancer. The ability to predict tumour response would allow chemotherapy administration to be directed towards only those patients who would benefit, thus maximising treatment efficiency. We aimed to identify putative protein biomarkers associated with chemotherapy resistance, using fresh tumour samples with antibody microarray analysis and then to perform pilot clinical validation experiments.

Materials and methods

Chemotherapy resistant and chemotherapy sensitive tumour samples were collected from breast cancer patients who had received anthracycline based neoadjuvant therapy consisting of epirubicin with cyclophosphamide followed by docetaxel. A total of 5 comparative proteomics experiments were performed using invasive ductal carcinomas which demonstrated estrogen receptor positivity (luminal subtype). Protein expression was compared between chemotherapy resistant and chemotherapy sensitive tumour samples using the Panorama XPRESS Profiler725 antibody microarray containing 725 antibodies from a wide variety of cell signalling and apoptosis pathways. A pilot series of archival samples was used for clinical validation of putative predictive biomarkers.

Results

AbMA analysis revealed 38 differentially expressed proteins which demonstrated at least 1.8 fold difference in expression in chemotherapy resistant tumours and 7 of these proteins (Zyxin, 14-3-3 theta/tau, tBID, Pinin, Bcl-xL, RIP and MyD88) were found in at least 2 experiments. Clinical validation in a pilot series of archival samples revealed 14-3-3 theta/tau and tBID to be significantly associated with chemotherapy resistance.

Conclusions

For the first time, antibody microarrays have been used to identify proteins associated with chemotherapy resistance using fresh breast cancer tissue. We propose a potential role for 14-3-3 theta/tau and tBID as predictive biomarkers of neoadjuvant chemotherapy resistance in breast cancer. Further validation in a larger sample series is now required.     

Pilot and feasibility study: comparative proteomic analysis by 2-DE MALDI TOF/TOF MS reveals 14-3-3 proteins as putative biomarkers of response to neoadjuvant chemotherapy in ER-positive breast cancer

Neoadjuvant chemotherapy is used to treat oestrogen receptor-positive breast cancer however chemo-resistance is a major obstacle in this molecular subtype. The ability to predict tumour response would allow chemotherapy administration to be directed towards patients who would most benefit, thus maximising treatment efficacy. We aimed to identify protein biomarkers associated with response to neoadjuvant chemotherapy, in a pilot study using comparative 2-DE MALDI TOF/TOF MS proteomic analysis of breast tumour samples. A total of 3 comparative proteomic experiments were performed, comparing protein expression between chemotherapy-sensitive and chemotherapy-resistant oestrogen receptor-positive invasive ductal carcinoma tissue samples. This identified a list of 132 unique proteins that were significantly differentially expressed (≥ 2 fold) in chemotherapy resistant samples, 57 of which were identified in at least two experiments. Ingenuity? Pathway Analysis was used to map the 57 DEPs onto canonical signalling pathways. We implicate several isoforms of 14-3-3 family proteins (theta/tau, gamma, epsilon, beta/alpha and zeta/delta), which have previously been associated with chemotherapy resistance in breast cancer. Extensive clinical validation is now required to fully assess the role of these proteins as putative markers of chemotherapy response in luminal breast cancer subtypes.     

Landscape host abundance and configuration regulate periodic outbreak behavior in spruce budworm Choristoneura fumiferana

Landscape‐level forest management has long been hypothesized to affect forest insect outbreak dynamics, but empirical evidence remains elusive. We hypothesized that the combination of increased hardwood relative to host tree species, prevalence of younger forests, and fragmentation of those forests due to forest harvesting legacies would reduce outbreak intensity, increase outbreak frequency, and decrease spatial synchrony in spruce budworm Choristoneura fumiferana outbreaks. We investigated these hypotheses using tree ring samples collected across 51 sites pooled into 16 subareas distributed across a large ecoregion spanning the international border between Ontario (Canada), and Minnesota (USA). This ecoregion contains contrasting land management zones with clear differences in forest landscape structure (i.e. forest composition and spatial configuration) while minimizing the confounding influence of climate. Cluster analyses of the 76‐yr time‐series generally grouped by subareas found within the same land management zone. Spatial nonparametric covariance analysis indicated that the highest and lowest degree of spatial synchrony of spruce budworm outbreaks were found within unmanaged wilderness and lands managed at fine spatial scales in Minnesota, respectively. Using multivariate analysis, we also found that forest composition, configuration, and climate together accounted for a total of 40% of the variance in outbreak chronologies, with a high level of shared variance between composition and configuration (13%) and between composition and climate (9%). At the scale of our study, climate on its own did not explain any of the spatial variation in outbreaks. Outbreaks were of higher frequency, lower intensity, and less spatially synchronized in more fragmented, younger forests with a lower proportion of host species, with opposing outbreak characteristics observed in regions characterised by older forests with more concentrated host species. Our study is the first quantitative evaluation of the long‐standing ‘silvicultural hypothesis’ of spruce budworm management specifically conducted at a spatio‐temporal scale for which it was intended.     

Comparing the effects of even‐ and uneven‐aged silviculture on ecological diversity and processes: A review

With an increasing pressure on forested landscapes, conservation areas may fail to maintain biodiversity if they are not supported by the surrounding managed forest matrix. Worldwide, forests are managed by one of two broad approaches—even‐ and uneven‐aged silviculture. In recent decades, there has been rising public pressure against the systematic use of even‐aged silviculture (especially clear‐cutting) because of its perceived negative esthetic and ecological impacts. This led to an increased interest for uneven‐aged silviculture. However, to date, there has been no worldwide ecological comparison of the two approaches, based on multiple indicators. Overall, for the 99 combinations of properties or processes verified (one study may have evaluated more than one property or process), we found nineteen (23) combinations that clearly showed uneven‐aged silviculture improved the evaluated metrics compared to even‐aged silviculture, eleven (16) combinations that showed the opposite, and 60 combinations that were equivocal. Furthermore, many studies were based on a limited study design without either a timescale (44 of the 76) or spatial (54 of the 76) scale consideration. Current views that uneven‐aged silviculture is better suited than even‐aged silviculture for maintaining ecological diversity and processes are not substantiated by our analyses. Our review, by studying a large range of indicators and many different taxonomic groups, also clearly demonstrates that no single approach can be relied on and that both approaches are needed to ensure a greater number of positive impacts. Moreover, the review clearly highlights the importance of maintaining protected areas as some taxonomic groups were found to be negatively affected no matter the management approach used. Finally, our review points to a lack of knowledge for determining the use of even‐ or uneven‐aged silviculture in terms of both their respective proportion in the landscape and their spatial agency.     

Canopy and age structures of some old sub-boreal Picea stands in British Columbia

Abstract. 14 old, unlogged, Picea-dominated stands in the moist cool Sub-Boreal Spruce biogeoclimatic subzone of central British Columbia, Canada, were sampled to describe canopy heterogeneity, regeneration patterns and tree population age structures. These stands are composed of Picea engelmannii × glauca hybrids, Abies lasiocarpa and lesser amounts of Pinus contorta and Populus tremuloides, and had survived 124–343 yr since the last stand-destroying wildfire. Canopy cover was patchy and highly variable (ranging from 30.5 % to 86.4 %) but was not significantly related to stand age. Vertical canopy structure was less variable, reflecting the shade-tolerance and live crown ratios (length of live canopy expressed relative to tree height) of component species: 18.8 % for Populus, 20.2 % for Pinus, 46.7 % for Picea and 51.4 % for Abies. Individual stands varied considerably in their population structures and in their stand development trajectories, yet some patterns are evident. Survivors of the initial post-disturbance cohort of trees took 51 to 118 yr (mean = 80, s.d. = 20) to establish. Some stands had all tree species present during stand initiation, while other stands indicated early successional roles for Populus and Pinus, or a late successional role for Abies. Abies recruitment, while often slow in the beginning, occurs uniformly throughout the history of most stands, reflecting the high shade-tolerance of this species. Picea is often recruited in high densities early in stand development, and then (after long periods of exclusion) may be displaced by Abies in some stands but maintains itself in others. Minor, single-tree disturbances (due to bark beetles, root rot, and windthrow) were important in accelerating the reinitiation of Picea in the understory. Results thus suggest that stands from this region can be self-perpetuating in the absence of fire. Yet, post-fire tree populations still clearly dominate these spruce-fir forests, for only the oldest stand had greater basal area in the replacement cohort than in the initial cohort.     

The Effects of Spatial Legacies following Shifting Management Practices and Fire on Boreal Forest Age Structure

Forest age structure and its spatial arrangement are important elements of sustainable forestry because of their effects on biodiversity and timber availability. Forest management objectives that include specific forest age structure may not be easily attained due to constraints imposed by the legacies of historical management and natural disturbance. We used a spatially explicit stochastic model to explore the synergetic effects of forest management and fire on boreal forest age structure. Specifically, we examined (1) the duration of spatial legacies of different management practices in the boreal forest, (2) how multiple shifts in management practices affect legacy duration and the spatial trajectories of forest age structure, and (3) how fire influences legacy duration and pattern development in combination with harvesting. Results based on 30 replicates of 500 years for each scenario indicate that (1) spatial legacies persist over 200 years and the rate at which legacies are overcome depends on whether new management targets are in synchrony with existing spatial pattern; (2) age specific goals were met faster after multiple management shifts due to the similar spatial scale of the preceding management types; (3) because large fires can erase the spatial pattern created by smaller disturbances, scenarios with fire had shorter lags than scenarios without fire. These results suggest that forest management goals can be accelerated by applying management at a similar spatial scale as existing spatial patterns. Also, management planning should include careful consideration of historical management as well as current and likely future disturbances.     

Resistance,Resilience or Change: Post-disturbance Dynamics of Boreal Forests After Insect Outbreaks

Ecosystems - Understanding and measuring forest resistance and resilience have emerged as key priorities in ecology and management, particularly to maintain forest functioning. The analysis of the...