FIRE IS A MAJOR DISTURBANCE AFFECTING ECOSYSTEMS WORLDWIDE. PHYLOGENETIC STUDIES HAVE SHOWN THAT THE EVOLUTION OF SEED PERSISTENCE (FIRE RESISTANCE) IS ASSOCIATED WITH FIRE FREQUENCY OR SEVERITY. HOWEVER, THE EXISTENCE OF SPECIFIC SEED TRAITS RESULTING FROM NATURAL SELECTION MEDIATED BY FIRE REMAINS A KEY QUESTION IN PLANT EVOLUTION. WE EVALUATED THE ROLE OF FIRE IN THE EVOLUTION OF SEED TRAITS FROM A MICROEVOLUTIONARY PERSPECTIVE, USING AS A STUDY SYSTEM A NATIVE FORB FROM THE CHILEAN MATORRAL, WHERE FIRE IS A NOVEL, ANTHROPOGENIC DISTURBANCE. WE SHOW THAT ANTHROPOGENIC FIRES ARE SHAPING THE EVOLUTION OF SEED TRAITS SUCH AS PUBESCENCE AND SHAPE. AMONG-POPULATION VARIATION IN SEED PUBESCENCE, SHAPE, AND PERICARP THICKNESS WAS STRONGLY ASSOCIATED WITH FIRE FREQUENCY, AND WITHIN A POPULATION, FIRE SELECTED THOSE PLANTS WITH MORE PUBESCENT SEEDS, THICKER PERICARPS, AND LESS ROUNDED SEEDS. SEED PUBESCENCE AND SHAPE WERE SHOWN TO BE HERITABLE TRAITS. OUR FINDINGS PROVIDE INSIGHTS INTO THE UNDERSTANDING OF THE EVOLUTION OF SEED TRAITS IN FIRE-PRONE ENVIRONMENTS AND DEMONSTRATE THAT HUMAN-MADE FIRES CAN BE DRIVING EVOLUTIONARY CHANGES IN PLANT SPECIES FROM ECOSYSTEMS WHERE FIRES DO NOT OCCUR NATURALLY.

AIM WE TESTED THE HYPOTHESIS THAT ANTHROPOGENIC FIRES FAVOUR THE SUCCESSFUL ESTABLISHMENT OF ALIEN ANNUAL SPECIES TO THE DETRIMENT OF NATIVES IN THE CHILEAN COASTAL MATORRAL. LOCATION VALPARAÍSO REGION, CENTRAL CHILE. METHODS WE SAMPLED SEED RAIN, SEEDBANK EMERGENCE AND ESTABLISHMENT OF SPECIES IN FOUR PAIRED BURNED AND UNBURNED AREAS AND COMPARED (USING GLMM) FIRE RESISTANCE AND PROPAGULE ARRIVAL OF ALIEN AND NATIVE SPECIES. TO ASSESS THE RELATIVE IMPORTANCE OF SEED DISPERSAL AND SEEDBANK SURVIVAL IN EXPLAINING PLANT ESTABLISHMENT AFTER FIRE, WE COMPARED SEED RAIN AND SEEDBANK STRUCTURE WITH POST-FIRE VEGETATION USING ORDINATION ANALYSES. RESULTS FIRE DID NOT CHANGE THE PROPORTION OF ALIEN SPECIES IN THE COASTAL MATORRAL. HOWEVER, FIRE INCREASED THE NUMBER OF ANNUAL SPECIES (NATIVES AND ALIENS) OF WHICH 87% WERE ALIENS. FIRE REDUCED THE ALIEN SEEDBANK AND NOT THE NATIVE SEEDBANK, BUT ALIEN SPECIES REMAINED DOMINANT IN BURNED SOIL SAMPLES (66% OF THE TOTAL SPECIES RICHNESS). SEED RAIN WAS HIGHER FOR ALIEN ANNUALS THAN FOR NATIVE ANNUALS OR PERENNIALS, THUS CONTRIBUTING TO THEIR ESTABLISHMENT AFTER FIRE. NEVERTHELESS, SEED RAIN WAS LESS IMPORTANT THAN SEEDBANK SURVIVAL IN EXPLAINING PLANT ESTABLISHMENT IN BURNED AREAS.

THE BIOGEOCHEMICAL CYCLES OF CARBON (C), NITROGEN (N) AND PHOSPHORUS (P) ARE INTERLINKED BY PRIMARY PRODUCTION, RESPIRATION AND DECOMPOSITION IN TERRESTRIAL ECOSYSTEMS1. IT HAS BEEN SUGGESTED THAT THE C, N AND P CYCLES COULD BECOME UNCOUPLED UNDER RAPID CLIMATE CHANGE BECAUSE OF THE DIFFERENT DEGREES OF CONTROL EXERTED ON THE SUPPLY OF THESE ELEMENTS BY BIOLOGICAL AND GEOCHEMICAL PROCESSES1,2,3,4,5. CLIMATIC CONTROLS ON BIOGEOCHEMICAL CYCLES ARE PARTICULARLY RELEVANT IN ARID, SEMI-ARID AND DRY SUB-HUMID ECOSYSTEMS (DRYLANDS) BECAUSE THEIR BIOLOGICAL ACTIVITY IS MAINLY DRIVEN BY WATER AVAILABILITY6,7,8. THE INCREASE IN ARIDITY PREDICTED FOR THE TWENTY-FIRST CENTURY IN MANY DRYLANDS WORLDWIDE9,10,11 MAY THEREFORE THREATEN THE BALANCE BETWEEN THESE CYCLES, DIFFERENTIALLY AFFECTING THE AVAILABILITY OF ESSENTIAL NUTRIENTS12,13,14. HERE WE EVALUATE HOW ARIDITY AFFECTS THE BALANCE BETWEEN C, N AND P IN SOILS COLLECTED FROM 224 DRYLAND SITES FROM ALL CONTINENTS EXCEPT ANTARCTICA. WE FIND A NEGATIVE EFFECT OF ARIDITY ON THE CONCENTRATION OF SOIL ORGANIC C AND TOTAL N, BUT A POSITIVE EFFECT ON THE CONCENTRATION OF INORGANIC P. ARIDITY IS NEGATIVELY RELATED TO PLANT COVER, WHICH MAY FAVOUR THE DOMINANCE OF PHYSICAL PROCESSES SUCH AS ROCK WEATHERING, A MAJOR SOURCE OF P TO ECOSYSTEMS, OVER BIOLOGICAL PROCESSES THAT PROVIDE MORE C AND N, SUCH AS LITTER DECOMPOSITION12,13,14. OUR FINDINGS SUGGEST THAT ANY PREDICTED INCREASE IN ARIDITY WITH CLIMATE CHANGE WILL PROBABLY REDUCE THE CONCENTRATIONS OF N AND C IN GLOBAL DRYLANDS, BUT INCREASE THAT OF P. THESE CHANGES WOULD UNCOUPLE THE C, N AND P CYCLES IN DRYLANDS AND COULD NEGATIVELY AFFECT THE PROVISION OF KEY SERVICES PROVIDED BY THESE ECOSYSTEMS.

COLONISING POPULATIONS DO NOT ALWAYS EXHIBIT FOUNDER EFFECTS. COMMON EXPLANATIONS ARE HIGH LEVELS OF IMMIGRATION AND/OR REPRODUCTION, BUT FEW EMPIRICAL TESTS HAVE BEEN DONE. WE MEASURED GENETIC DIVERSITY OF NASSAUVIA ARGENTEA IN TERMS OF VARIATION AND DIVERGENCE OF PLANT POPULATIONS THAT HAVE COLONISED VOLCÁN LONQUIMAY, CHILE, FOLLOWING ITS LATEST ERUPTION IN 1988. FIFTEEN INDIVIDUALS FROM EACH OF TEN POPULATIONS WERE ANALYSED USING AMPLIFIED FRAGMENT LENGTH POLYMORPHISM (AFLP) MARKERS. GENETIC VARIATION AND DIVERGENCE WERE LOWER IN COLONISING POPULATIONS THAN ESTABLISHED ONES, BUT NOT SIGNIFICANTLY SO (ANOVA AND KRUSKAL-WALLIS TESTS, P < 0.05). NO CONSISTENT OR SIGNIFICANT TRENDS WERE OBTAINED FROM REGRESSIONS WITH DEMOGRAPHIC VARIABLES. BAYESIAN ANALYSIS OF POPULATION STRUCTURE REVEALS CLOSE RELATEDNESS AMONG POPULATIONS OF ALL AGES ON THE VOLCANO. WE CONCLUDED THAT NO CONSPICUOUS FOUNDER EFFECT HAS OCCURRED IN THE GENETIC DIVERSITY OF POPULATIONS COLONISING A NEWLY DERIVED VOLCANIC ENVIRONMENT. AN IMPORTANT IMPLICATION OF THIS IS THE ROLE OF PROXIMITY TO SOURCE REGIONS AND SPECIES VIGOUR IN MOULDING GENETIC DIVERSITY OF COLONISERS FROM DIFFERENT SPECIES.

EXPERIMENTS SUGGEST THAT BIODIVERSITY ENHANCES THE ABILITY OF ECOSYSTEMS TO MAINTAIN MULTIPLE FUNCTIONS, SUCH AS CARBON STORAGE, PRODUCTIVITY, AND THE BUILDUP OF NUTRIENT POOLS(MULTIFUNCTIONALITY). HOWEVER, THE RELATIONSHIP BETWEEN BIODIVERSITY AND MULTIFUNCTIONALITY HAS NEVER BEEN ASSESSED GLOBALLY IN NATURAL ECOSYSTEMS. WE REPORT HERE ON A GLOBAL EMPIRICAL STUDY RELATING PLANT SPECIES RICHNESS AND ABIOTIC FACTORS TO MULTIFUNCTIONALITY IN DRYLANDS, WHICH COLLECTIVELY COVER 41% OF EARTHS LAND SURFACE AND SUPPORT OVER 38% OF THE HUMAN POPULATION. MULTIFUNCTIONALITY WAS POSITIVELY AND SIGNIFICANTLY RELATED TO SPECIES RICHNESS. THE BEST-FITTING MODELS ACCOUNTED FOR OVER 55% OF THE VARIATION IN MULTIFUNCTIONALITY AND ALWAYS INCLUDED SPECIES RICHNESS AS A PREDICTOR VARIABLE. OUR RESULTS SUGGEST THAT THE PRESERVATION OF PLANT BIODIVERSITY IS CRUCIAL TO BUFFER NEGATIVE EFFECTS OF CLIMATE CHANGE AND DESERTIFICATION IN DRYLANDS.

QUESTIONS IS THE MACROLICHEN USNEA ANTARCTICA A ?NURSE? SPECIES TO ANTARCTIC FLORA? ARE POSITIVE PLANT?PLANT INTERACTIONS MORE FREQUENT THAN NEGATIVE INTERACTIONS IN ANTARCTIC ECOSYSTEMS? ARE MICROCLIMATIC MODIFICATIONS BY CUSHIONS OF U. ANTARCTICA RESPONSIBLE FOR THE NURSE EFFECT? LOCATION TWO SITES IN ANTARCTICA: KING GEORGE ISLAND, SOUTH SHETLAND (62°11? S, 58°56? W; 62°11? S, 58°59? W). METHODS WE EVALUATED THE ASSOCIATION OF PLANT SPECIES WITH U. ANTARCTICA CUSHIONS BY RECORDING SPECIES GROWING ? IN EQUIVALENT AREAS ? WITHIN AND OUTSIDE U. ANTARCTICA CUSHIONS. ADDITIONALLY, WE PERFORMED TRANSPLANT EXPERIMENTS WITH DESCHAMPSIA ANTARCTICA INDIVIDUALS TO ASSESS IF U. ANTARCTICA CUSHIONS ENHANCE PLANT SURVIVAL. IN BOTH STUDY SITES WE MONITORED TEMPERATURE, MOISTURE AND NUTRIENT STATUS OF SOIL OUTSIDE AND WITHIN THE CUSHIONS TO PROVIDE INSIGHTS INTO POTENTIAL MECHANISMS UNDERLYING POSSIBLE INTERACTIONS BETWEEN U. ANTARCTICA AND OTHER PLANT SPECIES. RESULTS EIGHT OUT OF 13 SPECIES WERE POSITIVELY ASSOCIATED WITH CUSHIONS OF THE WIDESPREAD LICHEN U. ANTARCTICA, WHILE ONLY ONE SPECIES (U. AURANTIACO-ATRA) SHOWED A NEGATIVE ASSOCIATION WITH U. ANTARCTICA. SURVIVAL OF DESCHAMPSIA WAS ENHANCED WHEN GROWING ASSOCIATED WITH U. ANTARCTICA CUSHIONS. OUR RESULTS INDICATE THAT CUSHIONS AMELIORATED THE EXTREME CONDITIONS OF ANTARCTIC ISLANDS THROUGH INCREASED TEMPERATURE AND SOIL MOISTURE, DECREASED RADIATION AND EVAPORATIVE WATER LOSS AND INCREASED NUTRIENT AVAILABILITY. CONCLUSIONS THE NURSE EFFECT OF U. ANTARCTICA IS VERIFIED. CUSHIONS OF THIS MACROLICHEN MAY BE A KEY COMPONENT IN STRUCTURING THE ANTARCTIC LANDSCAPE AND MAINTAINING LOCAL SPECIES RICHNESS, AND THEIR PRESENCE MIGHT INFLUENCE RANGE EXPANSION OF OTHER SPECIES.

THE NICHE OPPORTUNITY HYPOTHESIS PROPOSES THAT ALIEN PLANT ESTABLISHMENT IS GENERALLY DRIVEN BY THE INTEGRATED EFFECTS OF ENVIRONMENTAL CONDITIONS, CHANGES IN RESOURCE AVAILABILITY AND REDUCED HERBIVORY PRESSURE, BUT THERE IS YET LITTLE EVIDENCE SUPPORTING SUCH A COMPLEX INTERACTION IN NATURE. WE EVALUATED THE INTERACTIVE EFFECTS OF SOIL DISTURBANCE BY THE NATIVE FOSSORIAL MAMMAL SPALACOPUS CYANUS, MICROHABITAT (BENEATH SHRUBS AND OPEN AREAS), AND INTRODUCED HERBIVORES (RABBIT, ORYCTOLAGUS CUNICULUS) ON THE ESTABLISHMENT (SEEDLING EMERGENCE, ADULT ABUNDANCE, ABOVEGROUND BIOMASS, AND REPRODUCTIVE EFFORT) OF THE ALIEN ANNUAL PLANT FUMARIA CAPREOLATA IN A COASTAL MATORRAL OF CENTRAL CHILE. IN THE ABSENCE OF DISTURBANCE, SEEDLING EMERGENCE AND PLANT ESTABLISHMENT OF F. CAPREOLATA WAS LARGELY RESTRICTED TO UNDERSTORY MICROHABITATS. SOIL DISTURBANCE BY S. CYANUS SIGNIFICANTLY INCREASED SEEDLING EMERGENCE AND ESTABLISHMENT, BOTH BENEATH SHRUBS AND IN OPEN AREAS. THERE WAS NO EFFECT OF HERBIVORE EXCLUSION ON THE ABUNDANCE, BIOMASS AND REPRODUCTIVE EFFORT OF F. CAPREOLATA, ALTHOUGH THE BIOMASS OF OTHER CO-EXISTING SPECIES WAS REDUCED. OVERALL, THESE RESULTS SUGGEST THAT NATIVE FOSSORIAL MAMMALS MAY FAVOR THE INVASION OF F. CAPREOLATA BY ALLOWING MICROHABITAT EXPANSION INTO OPEN AREAS AND BY INCREASING ITS PERFORMANCE IN THOSE MICROHABITATS ALREADY OCCUPIED. WE SHOW HOW THE INTERPLAY BETWEEN SOIL DISTURBANCE, MICROHABITAT, AND REDUCED HERBIVORY MAY EXPLAIN INVASION PATTERNS AT THE LOCAL SCALE IN NATURAL COMMUNITIES.