Georgia R. Koerber

A putative hybrid of Eucalyptus largiflorens growing on salt- and drought-affected floodplains has reduced specific leaf area and leaf nitrogen

AputativehybridbetweenEucalyptuslargiflorensF.Muell.andEucalyptusgracilisF.Muell.,calledgreenbox, hasattractedattentionforitsabilitytogrowonthesalt-anddrought-affectedChowilla floodplainoftheMurrayRiverinSouth Australia. Relationships between carbon isotope discrimination (D 13 C) and the ratio of substomatal to ambient CO2 (ci/ca) indicated that green box was not as water use efficient as E. largiflorens. Specific leaf area of green box and E. gracilis was significantly lower compared with E. largiflorens (38.38 and 36.96 versus 43.71cm 2 g -1 ). Leaf nitrogen for green box and E.graciliswassignificantlylowercomparedwithE.largiflorens(12.66and11.35versus15.07mgg -1 dryweight,P=0.004 and 0.001,respectively) and leaf carbon ofE.gracilis was significantly higher compared with green box andE.largiflorens (541.75versus514.90and519.82mgg -1 dryweight,P=0.002and0.011respectively).Thereweresignificantly(P=0.016) more occurrences of elevated ci/ca below a minimum gs in E. gracilis compared with E. largiflorens, with green box being intermediate (means=21.6, 6.8 and 9.4). After 10 years, E. largiflorens trunk circumference had significantly increased (P=0.017)andheighthadsignificantlydecreased(P=0.026)duetovisibledieback.GreenboxandE.gracilisgrewslower, conserving resources, illustrating a useful strategy to consider when choosing plants for revegetation efforts.

Morphology, physiology and AFLP markers validate that green box is a hybrid of Eucalyptus largiflorens and E. gracilis (Myrtaceae)

Abstract. Prolonged drought and salinity on the Chowilla floodplain of the Murray River have caused deterioration of E. largiflorens F.Muell. A putative hybrid with E. gracilis F.Muell, green box, withstands the saline conditions. We aimed to substantiate that green box is a hybrid and to test for agreement between morphological and physiological characters with amplified fragment length polymorphisms (AFLP). Mature stands were measured for leaf, trunk, floral, cotyledon, carbon and nitrogen isotope discrimination, specific leaf area (SLA) and AFLP. Green box was placed between E. largiflorens and E. gracilis according to categorical principal components analysis (CATPCA) of 21 morphological and physiological characters and character states. The hybrid index of 11 AFLP markers that were 78% species specific separated E. gracilis and E. largiflorens, and the majority of green box plants displayed indices ranging from 0.42 to 0.53, reflecting mostly additive inheritance. Calculation of the hybrid index with all 232 AFLP markers, using maximum likelihood, similarly placed green box between E. gracilis and E. largiflorens. Our morphological, physiological and AFLP-marker observations substantiated that green box is a hybrid between E. largiflorens and E. gracilis.

Response of microbial activity to labile C addition in sandy soil from semi-arid woodland is influenced by vegetation patch and wildfire

Nutrient cycling in semi-arid woodlands is likely to be influenced by patchy vegetation, wildfire and the supply of easily available organic C, e.g. root exudates. The study assessed the effect of wildfire and vegetation patch on response of microbial activity to labile C addition in soil from a semi-arid Eucalyptus woodland. Two sites were studied: one unburnt and the other exposed to wildfire four-month before sampling. Top soil (0 – 30 cm) from under trees, under shrubs or in open areas from each site was air-dried and sieved to < 2 mm. The soils were incubated at 80% of maximum water holding capacity for 24 days without or with addition of 5 g C kg-1 as glucose. Soil organic carbon (TOC), microbial biomass C, N and P availability and cumulative respiration were greater under trees than in open areas. Fire decreased TOC and cumulative respiration only under trees and had little effect on available N, microbial biomass C and P concentrations. The greater increase in cumulative respiration by glucose addition under shrubs and in open areas compared to under trees and, in a given patch, greater in burnt than unburnt soils, indicate lower availability of native organic carbon.

Statistical associations between morphology, physiology and AFLP DNA markers enable selection of a putative eucalypt hybrid able to tolerate salt affected floodplains

Abstract A naturally occurring putative hybrid between Eucalyptus largiflorens F. Muell and Eucalyptus gracilis F. Muell called Green Box tolerates saline conditions of the River Murray floodplains better than E. largiflorens. Revegetation strategies utilizing seedlings of Green Box have had limited success because only a few are Green Box and the majority are throw backs to E. gracilis and E. largiflorens. Therefore, the purpose of this study was to identify traits characteristic of Green Box and AFLP markers associated with the traits enabling selection at the seedling stage. This was done by non-linear canonical correlation analysis (OVERALS) to test for statistically significant associations between morphological and physiological traits with 232 AFLP markers from 9 primer combinations. OVERALS with all markers produced 1st and 2nd dimensions accounting for 80 and 74% of variation respectively. Green Box plants were placed intermediate between E. gracillis and E. largiflorens according to leaf colour, gloss and nitrogen with component loadings (lc) of 0.340, 0.615 and 0.294 respectively. A second approach of simple linear regression of morphological and physiological traits against all 232 AFLP markers singled out 17 with significance P<0.05. Thirteen of these were also identified by OVERALS. Four occurred with high frequency in Green Box and E. largiflorens distinguishing them from E. gracilis. In order to separate Green Box and E. largiflorens, the segregation of a further three markers can be used to align Green Box with E. gracilis. Therefore, the segregation of 7 markers can be utilized to select Green Box.